Apparatus and method for controlling an operation of a plurality of communication layers

ABSTRACT

An apparatus for controlling an operation of a plurality of communication layers in a layered communication system provides a property of the communication channel, and includes a storage element for storing a first plurality of sets of parameters defining operation modes of a first communication layer of the plurality of communication layers and for providing a second plurality of sets of parameters defining operation modes of a second communication layer of the plurality of communication layers, a selector for selecting a first set of parameters from the first plurality of sets of parameters and for selecting a second set of parameters from the second plurality of sets of parameters in dependence-on the channel property and an optimization goal and provides the first set of parameters to the first communication layer and the second set of parameters to the second communication layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of copending InternationalApplication No. PCT/EP2003/011446, filed Oct. 15, 2003, which designatedthe United States, and was not published in English and is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of telecommunications and, inparticular, in the field of communication systems using protocol layersfor processing information to be transmitted and/or for processingreceived information.

2. Description of Prior Art

In mobile wireless communication environment it is a challenging task toprovide reliable high-quality services due to a dynamic behavior of acommunication link, for example of a wireless link. Therefore, systemdesigners have to cope with a non-predictable variation of transmissionquality resulting from time-varying resource availability, fadingerrors, outages or handover. For wireless networks beyond the thirdgeneration systems (B3G), this dynamic behavior will negatively beaffected since B3G systems are expected to span across heterogeneouswireless access network technologies with different transmissioncharacteristics. However, the next generation wireless networks areexpected to provide reliable and transparent services to the customersso that a seamless use of the network's diversity can be achieved.

Service and application provisioning in B3G does not only have to regardnetwork's density but also application diversity as new business modelswhich are expected to allow third party providers to offer theirapplication on top of the operators' service platforms making use ofadvanced open interfaces. In order to take dynamically changingapplication requirements into account, which may result e.g. fromvarying user preferences or varying user context, the operators willneed an ability to dynamically change the systems parameters in order toreact to the varying requirements.

Usually, conventional communication systems apply a plurality ofcommunication layers arranged to a protocol stack for informationprocessing. FIG. 9 shows a protocol stack comprising a plurality ofhierarchically arranged communication layers. The prior art protocolstack shown in FIG. 9 is disclosed in Andrew Tannenbaum, ComputerNetworks, 4^(th) Edition, Francis Hall, 2003.

The protocol stack comprises a physical layer 901, a data link layer 903arranged above the physical layer 901, a network layer 905 arranged ontop of the data link layer 903, a transport layer 907 arranged at top ofthe network layer 905, and an application layer 911 arranged at top ofthe transport layer 907.

Generally speaking, the application layer is operative for managing theinformation to be transmitted. For example, the information comprises amedia data stream, for example a video data stream, as information to betransmitted through a communication channel. Alternatively, theinformation may comprise a multimedia data stream consisting of videoand audio information, to be transmitted through the communicationchannel. Furthermore, the application may comprise an electronic mail,etc. In other words, the application layer is operative for transformingthe application to be transmitted into a transmittable informationstream.

The application layer 911 directly communicates with the transport layer907 being operative for providing a transport service, so that theinformation can be transmitted to a destination sink in dependency ofthe physical network used for communication. For example, the transportlayer appends a transport protocol data unit (TPDU) to the informationdata stream in order to preserve a peer-to-peer communication which iscommon in all communication networks. Peer-to-peer communication meansthat for example the transport layer 907 communicates directly withanother transport layer implemented in a destination network.

The transport layer 907 communicates directly with the network layer 905being operative for processing an information frame provided by thetransport layer 907, so that an end-to-end communication, i.e.communication between two computer entities, is possible.

The network layer 905 provides a network layer frame to a link layercomprising the data link layer 903 and the physical layer 901, whereinthe data link layer 903 and the physical layer 901 may comprise aplurality of sub-layers, for example a medium access control sub-layer.

The link layer is operative for managing the transmission of theinformation represented by bits through the communication channel. Forexample, the data link layer 903 is operative for applying a forwarderror correction encoding (FEC) or forward error detection encoding, forre-transmission of erroneous data frames (packets) and, for example, forconfirming of a correct reception of each frame by sending anacknowledgement frame. Furthermore, the data link layer 903 may beoperative for scheduling the frames to be transmitted in, for example, amulti-user scenario. Scheduling means, that a frame is transmitted at apredetermined time slot (transmission time frame).

The data link layer 903 directly communicates with the physical layer901 being operative for further encoding the streams provided by thedata link layer 903 by, for example, performing a modulation using amodulation scheme modulating a carrier according to the information tobe transmitted.

The embodiment of the protocol stack shown in FIG. 9 corresponds to aTCP/IP reference model described in the above-referenced document(TCP=transmission control protocol, IP=internet protocol). For the sakeof convenience it is to be noted, that the protocol stack shown in FIG.9 also corresponds to the OSI reference model (OSI=open systeminterconnect) with exception of two layers, namely a session layer and apresentation layer arranged between the application layer 901 and thetransport layer 907.

The internet protocol stack as depicted in FIG. 9 is expected to be usedas a basic platform for B3G systems and applications. However, in orderto achieve a good transmission quality, within a varying transmissionenvironment, an efficient use of the available network resources isnecessary in order to adapt the communication system or the applicationto come up, for example, to varying transmission characteristics andapplication requirements. For example, in case of a frequency-selectivecommunication channel, a suitable encoding of the data bit stream to betransmitted is necessary, so that a predetermined bit error probability,i.e. 10⁻⁶, is not increased. To do so, the physical layer may be, forexample, operative, to adapt the modulation scheme to the currentchannel characteristic. Accordingly, a system adaptation can beperformed on all protocol layers of the protocol stack by adapting therespective parameters determining an operation mode of a respectivecommunication layer.

Conventionally, the optimization of the system for a specificapplication, for example a video stream, is performed in a verticalmanner in a system carrying only one service in a non-layered scenario,e.g. in a POTS system (POTS=Plain Old Telephony Service).

In layered communication systems, such as wireless internet,traditionally, certain layers are independently optimized for anexpected worst case scenario (worst condition), which results in aninefficient use of the available communication resources, for example inavailable bandwidth, an achievable data rate associated with a certainbit error probability etc.

However, in existing systems, the intra-layer adaptation is performedwithout considering inter-layer dependencies. In P. A. Chou, and Z.Miao, “Rate-Distortion Optimization Streaming of Packetized Media”,Technical Report MSR-TR-2001-35, Microsoft Research, MicrosoftCorporation, February 2001, a communication system is disclosed, where amedia frame scheduling is performed by the application layer, whereinonly in inter-dependency of the media frames transporting video andaudio information is taken into account. In M. Kalman, E. Steinbach, andB. Girod, “R-D Optimized Media Streaming Enhanced with Adaptive MediaPlayout”, International Conference on Multimedia and Expo, ICME 2002,Lausanne, August 2002, an adaptive media playout scheme is described,where the playout speed of audio data (for example voice) and video datais varied as a function of channel conditions. In S. Saha, M. Jamtgaard,J. Villasenor, “Bringing the wireless Internet to mobile devices”,Computer, vol. 34, issue 6, pp. 54-58, June 2001, an adaptive middlelayer is described, that applies transcoding of media data in order toadapt the currently used coding scheme to varying channel conditions. InH. Imura et al., “TCP over Second (2.5G) and Third (3G) GenerationWireless Networks”, IETF RFC 3481, February 2003, a wireless TCPprotocol stack is described, that distinguishes between packet lossesdue to a network congestion and losses due to erasures on a wirelesslink. In F. H. Fitzek, and M. Reisslein, “A prefetching protocol forcontinuous media streaming in wireless environments”, IEEE Journal onSelected Areas in Communications, vol. 19, no. 10, pp. 2015-2028,October 2001, a data link layer re-transmission is described, where adelay constraint is taken into account. The known differentiatedservices approached (DIFFSERV) is based on an established priority amongmedia packets, so that more important media packets are preferablyscheduled. Additionally, adaptive modulation and encoding on thephysical layer is known, as for example described in the IEEE 802.11astandard.

However, the above indicated prior art approaches suffer from the fact,that only one layer is optimized with respect to fulfilling anoptimization goal. For example, in order to improve a transmissionquality, the physical layer may be operative to adaptively adjust thetransmission power depending on a current channel condition, for examplea current channel attenuation. In other words, the above indicated priorart approaches rely on an optimization of only one parameter setdetermining an operation mode of the respective communication layer.

In order to more efficiently exploit the resources, an adaptation of twolayers can be performed. In K. Stuhlmüller, N. Färber, and B. Girod,“Analysis of video transmission over lossy channels”, IEEE Journal onSelected Area in Communication, vol. 18, no. 6, pp. 1012-1032, June2000, and T. Fingscheidt, T. Hindelang, R. V. Cox, N. Seshadri, “JointSource-Channel (De)Coding for Mobile Communications”, IEEE Transactionson Communications, Vol. 50, No. 2, pp. 200-212, February 2002, a sourceand channel coding scheme is described. The adaptation scheme is basedon an adaptation of a source rate and code rate depending on the channelconditions in terms of transmission quality. To be more specific, ananalytic formula is disclosed enabling a calculating of a source rateand of a channel rate.

In W. Yuan, K. Nahrstedt, S. Adve, D. Jones, R. Kravets: Design andEvaluation of a Cross-Layer Adaptation Framework for Mobile MultimediaSystems, to appear in SPIE/ACM Multimedia Computing and NetworkingConference (MMCN) 2003, an optimization of power control andtransmission data rate is disclosed. In S. Toumpis, A. Goldsmith:Performance, Optimization, and Cross-Layer Design of Media AccessProtocols for Wireless Ad Hoc Networks, IEEE International Conference onCommunications (ICC), 2003 a medium access control (MAC) layer andphysical layer optimization for ad hoc networks are described.

However, the prior art concepts applying cross-layer design foroptimization purposes suffer from a disadvantage, that, within thecommunication system, only a certain optimization approach is consideredfor the intra-layer adaptation. Moreover, the prior art approaches donot consider inter-layer dependencies which results in an ineffectiveexploitation of the available resources.

A further disadvantage of the prior art approaches is that the disclosedoptimization schemes are not flexible. Since the prior art approachesindicated above only consider one or two certain parameters foroptimization, for example power control and transmission data rate,further optimization scenarios are not considered in order to fullyexploit the available communication resources.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a concept for anefficient cross-layer optimization for layered communication systems.

In accordance with a first aspect, the invention provides an apparatusfor controlling an operation of a plurality of communication layers in alayered communication system, the layered communication systemtransmitting information through a communication channel, wherein theinformation has a first information associated with a first user and asecond information associated with a second user in a multi-userscenario, wherein an operation of a first communication layer of theplurality of communication layers is determined by a first set ofparameters, and wherein an operation of a second communication layer ofthe plurality of communication layers is determined by a second set ofparameters, wherein the first communication layer is operative forencoding the first information to obtain a first information signal andfor encoding the second information to obtain a second informationsignal, wherein the second communication layer is operative for encodingthe first information signal and the second information signal to obtaina composite signal to be transmitted through the communication channel,the apparatus having:

-   a provider for providing a property of the communication channel;-   a storage element for storing a first plurality of sets of    parameters defining different operation modes of the first    communication layer and for providing a second plurality of sets of    parameters defining different operation modes of the second    communication layer;-   a selector for selecting a first set of parameters from the first    plurality of sets of parameters, and for selecting the second set of    parameters from the second plurality of sets of parameters, wherein    the selector is operative for selecting the first set of parameters    and the second set of parameters in dependence of the channel    property and an optimization goal, wherein the optimization goal is    an optimized transmission quality for the first information and for    the second information, and wherein the selector is operative for    jointly selecting the first set of parameters to be used by the    first communication layer for encoding the first information and the    second information, and the second set of parameters to be used by    the second communication layer for encoding the first information    signal and the second information signal to optimize the    transmission quality of the first information and of the second    information; and-   a provider for providing the first set of parameters to the first    communication layer and the second set of parameters to the second    communication layer.

In accordance with a second aspect, the invention provides acommunication apparatus for processing an information to be transmittedin accordance with a transmission protocol, the transmission protocolhaving a plurality of protocol layers, the communication apparatushaving:

-   an information source for providing the information;-   the apparatus for controlling an operation of a plurality of    communication layers in a layered communication system, the layered    communication system transmitting information through a    communication channel, wherein the information has a first    information associated with a first user and a second information    associated with a second user in a multi-user scenario, wherein an    operation of a first communication layer of the plurality of    communication layers is determined by a first set of parameters, and    wherein an operation of a second communication layer of the    plurality of communication layers is determined by a second set of    parameters, wherein the first communication layer is operative for    encoding the first information to obtain a first information signal    and for encoding the second information to obtain a second    information signal, wherein the second communication layer is    operative for encoding the first information signal and the second    information signal to obtain a composite signal to be transmitted    through the communication channel, the apparatus having:    -   a provider for providing a property of the communication        channel;    -   a storage element for storing a first plurality of sets of        parameters defining different operation modes of the first        communication layer and for providing a second plurality of sets        of parameters defining different operation modes of the second        communication layer;    -   a selector for selecting a first set of parameters from the        first plurality of sets of parameters, and for selecting the        second set of parameters from the second plurality of sets of        parameters, wherein the selector is operative for selecting the        first set of parameters and the second set of parameters in        dependence of the channel property and an optimization goal,        wherein the optimization goal is an optimized transmission        quality for the first information and for the second        information, and wherein the selector is operative for jointly        selecting the first set of parameters to be used by the first        communication layer for encoding the first information and the        second information, and the second set of parameters to be used        by the second communication layer for encoding the first        information signal and the second information signal to optimize        the transmission quality of the first information and of the        second information; and    -   a provider for providing the first set of parameters to the        first communication layer and the second set of parameters to        the second communication layer,-   for controlling the plurality of protocol layers;-   a processor for processing the information in accordance with the    protocol layers.

In accordance with a third aspect, the invention provides acommunication apparatus for processing a received signal in accordancewith a reception protocol, the received signal being a received versionof a transmit signal transmitted through a communication channel, thetransmit signal having an information processed in accordance with atransmission protocol, wherein the transmission protocol has a firsttransmission protocol layer and a second transmission protocol layer,wherein an operation mode of the first transmission protocol layer isdetermined by a first set of transmission parameters, wherein anoperation mode of the second transmission protocol layer is determinedby a second set of transmission parameters, wherein the first set oftransmission parameters and the second set of transmission parametersare pair-wise selected from a plurality of transmission parameters independence on a property of the communication channel, wherein thereception protocol has a first reception protocol layer and a secondreception protocol layer, wherein an operation mode of the firstreception protocol layer is determined by a first set of receptionparameters, and wherein an operation mode of the second receptionprotocol layer is determined by a second set of reception parameters,the apparatus having:

-   a storage element for storing a plurality of sets of reception    parameters, each set of reception parameters corresponding to a set    of transmit parameters;-   a provider for providing a transmission protocol information    indicating the pair of the first and second set of transmission    parameters used for processing the information before transmitting    the information;-   a selector for selecting a pair consisting of the first set of    reception parameters and the second set of reception parameters    corresponding to the pair of the first and the second set of    transmission parameters on the basis of the transmission protocol    information;-   a provider for providing a pair of the first set of reception    parameter and the second set of reception parameter to the first    reception protocol layer and to the second reception protocol layer;-   a processor for processing the receive signal in accordance with the    reception protocol to obtain the information.

In accordance with a fourth aspect, the invention provides a method forcontrolling an operation of a plurality of communication layers in alayered communication system, the layered communication systemtransmitting information through a communication channel, wherein theinformation has a first information associated with a first user and asecond information associated with a second user in a multi-userscenario, wherein an operation of a first communication layer of thefirst plurality of communication layers is determined by a first set ofparameters, and wherein a operation of a second communication layer ofthe plurality of communication layers is determined by a second set ofparameters, wherein the first communication layer is operative forencoding the first information to obtain a first information signal andfor encoding the second information to obtain a second informationsignal, wherein the second communication layer is operative for encodingthe first information signal and the second information signal to obtaina composite signal to be transmitted through the communication channel,the method including the steps of:

-   providing a property of the communication channel;-   storing a first plurality of sets of parameters defining different    operation modes of the first communication layer;-   providing a second plurality of sets of parameters defining    different operation modes of the second communication layer;-   jointly selecting the first set of parameters from the first    plurality of sets of parameters and the second set of parameters    from the second plurality of sets of parameters in dependence on the    channel property and an optimization goal, the first set of    parameters to be used by the first communication layer for encoding    the first information and the second information, and the second set    of parameters to be used by the second communication layer for    encoding the first information signal and the second information    signal to optimize the transmission quality of the first information    and of the second information, wherein the optimization goal is an    optimized transmission quality for the first information and for the    second information;-   providing the first set of parameters to the first communication    layer and the second set of parameters to the second communication    layer.

In accordance with a fifth aspect, the invention provides a method forprocessing an information to be transmitted in accordance with atransmission protocol, the transmission protocol having a plurality ofprotocol layers, the method including the steps of:

-   providing the information;-   controlling the plurality of protocol layers in accordance with the    method for controlling an operation of a plurality of communication    layers in a layered communication system, the layered communication    system transmitting information through a communication channel,    wherein the information has a first information associated with a    first user and a second information associated with a second user in    a multi-user scenario, wherein an operation of a first communication    layer of the first plurality of communication layers is determined    by a first set of parameters, and wherein a operation of a second    communication layer of the plurality of communication layers is    determined by a second set of parameters, wherein the first    communication layer is operative for encoding the first information    to obtain a first information signal and for encoding the second    information to obtain a second information signal, wherein the    second communication layer is operative for encoding the first    information signal and the second information signal to obtain a    composite signal to be transmitted through the communication    channel, the method including the steps of:    -   providing a property of the communication channel;    -   storing a first plurality of sets of parameters defining        different operation modes of the first communication layer;    -   providing a second plurality of sets of parameters defining        different operation modes of the second communication layer;    -   jointly selecting the first set of parameters from the first        plurality of sets of parameters and the second set of parameters        from the second plurality of sets of parameters in dependence on        the channel property and an optimization goal, the first set of        parameters to be used by the first communication layer for        encoding the first information and the second information, and        the second set of parameters to be used by the second        communication layer for encoding the first information signal        and the second information signal to optimize the transmission        quality of the first information and of the second information,        wherein the optimization goal is an optimized transmission        quality for the first information and for the second        information;    -   providing the first set of parameters to the first communication        layer and the second set of parameters to the second        communication layer;-   processing the information in accordance with the protocol layer.

In accordance with a sixth aspect, the invention provides a method forprocessing a received signal in accordance with a reception protocol,the received signal being a received version of a transmit signaltransmitted through a communication channel, the transmit signal havingan information processed in accordance with a transmission protocol,wherein the transmission protocol has a first transmission protocollayer and a second transmission protocol layer, wherein an operationmode of the first transmission protocol layer is determined by a firstset of parameters, wherein an operation mode of the second transmissionprotocol layer is determined by a second set of transmission parameters,wherein the first set of transmission parameters and the second set oftransmission parameters are pair-wise selected from a plurality oftransmission parameters in dependence on a property of the communicationchannel, wherein the reception protocol has a first reception protocollayer and a second reception protocol layer, wherein an operation modeof the first reception protocol layer is determined by a first set ofreception parameter, and wherein an operation mode of the secondreception protocol layer is determined by a second set of receptionparameters, the method including the steps of:

-   storing a plurality of sets of reception parameters, each set of    reception parameters corresponding to a set of transmission    parameters;-   providing a transmission protocol information indicating the pair of    first and second set of transmission parameters used for processing    the information before transmitting the information;-   selecting a pair consisting of the first set of reception parameters    and the second set of reception parameters corresponding to the pair    of the first and second set of transmission parameters on the basis    of the transmission protocol information;-   providing the pair of the first set of reception parameters and the    second set of reception parameters to the first reception protocol    layer and to the second reception protocol layer;-   processing the received signal in accordance with the reception    protocol to obtain the information.

In accordance with a seventh aspect, the invention provides a computerprogram having a program code for performing the method for controllingan operation of a plurality of communication layers in a layeredcommunication system, the layered communication system transmittinginformation through a communication channel, wherein the information hasa first information associated with a first user and a secondinformation associated with a second user in a multi-user scenario,wherein an operation of a first communication layer of the firstplurality of communication layers is determined by a first set ofparameters, and wherein a operation of a second communication layer ofthe plurality of communication layers is determined by a second set ofparameters, wherein the first communication layer is operative forencoding the first information to obtain a first information signal andfor encoding the second information to obtain a second informationsignal, wherein the second communication layer is operative for encodingthe first information signal and the second information signal to obtaina composite signal to be transmitted through the communication channel,the method including the steps of:

-   -   providing a property of the communication channel;    -   storing a first plurality of sets of parameters defining        different operation modes of the first communication layer;    -   providing a second plurality of sets of parameters defining        different operation modes of the second communication layer;    -   jointly selecting the first set of parameters from the first        plurality of sets of parameters and the second set of parameters        from the second plurality of sets of parameters in dependence on        the channel property and an optimization goal, the first set of        parameters to be used by the first communication layer for        encoding the first information and the second information, and        the second set of parameters to be used by the second        communication layer for encoding the first information signal        and the second information signal to optimize the transmission        quality of the first information and of the second information,        wherein the optimization goal is an optimized transmission        quality for the first information and for the second        information;    -   providing the first set of parameters to the first communication        layer and the second set of parameters to the second        communication layer,        when the program runs on a computer.

In accordance with a eighth aspect, the invention provides a computerprogram having a program code for performing the method for processingan information to be transmitted in accordance with a transmissionprotocol, the transmission protocol having a plurality of protocollayers, the method including the steps of:

-   -   providing the information;    -   controlling the plurality of protocol layers in accordance with        the method for controlling an operation of a plurality of        communication layers in a layered communication system, the        layered communication system transmitting information through a        communication channel, wherein the information has a first        information associated with a first user and a second        information associated with a second user in a multi-user        scenario, wherein an operation of a first communication layer of        the first plurality of communication layers is determined by a        first set of parameters, and wherein a operation of a second        communication layer of the plurality of communication layers is        determined by a second set of parameters, wherein the first        communication layer is operative for encoding the first        information to obtain a first information signal and for        encoding the second information to obtain a second information        signal, wherein the second communication layer is operative for        encoding the first information signal and the second information        signal to obtain a composite signal to be transmitted through        the communication channel, the method including the steps of:        -   providing a property of the communication channel;        -   storing a first plurality of sets of parameters defining            different operation modes of the first communication layer;        -   providing a second plurality of sets of parameters defining            different operation modes of the second communication layer;        -   jointly selecting the first set of parameters from the first            plurality of sets of parameters and the second set of            parameters from the second plurality of sets of parameters            in dependence on the channel property and an optimization            goal, the first set of parameters to be used by the first            communication layer for encoding the first information and            the second information, and the second set of parameters to            be used by the second communication layer for encoding the            first information signal and the second information signal            to optimize the transmission quality of the first            information and of the second information, wherein the            optimization goal is an optimized transmission quality for            the first information and for the second information;        -   providing the first set of parameters to the first            communication layer and the second set of parameters to the            second communication layer;    -   processing the information in accordance with the protocol        layer,        when the program runs on a computer.

In accordance with a ninth aspect, the invention provides a computerprogram having a program code for performing the method for processing areceived signal in accordance with a reception protocol, the receivedsignal being a received version of a transmit signal transmitted througha communication channel, the transmit signal having an informationprocessed in accordance with a transmission protocol, wherein thetransmission protocol has a first transmission protocol layer and asecond transmission protocol layer, wherein an operation mode of thefirst transmission protocol layer is determined by a first set ofparameters, wherein an operation mode of the second transmissionprotocol layer is determined by a second set of transmission parameters,wherein the first set of transmission parameters and the second set oftransmission parameters are pair-wise selected from a plurality oftransmission parameters in dependence on a property of the communicationchannel, wherein the reception protocol has a first reception protocollayer and a second reception protocol layer, wherein an operation modeof the first reception protocol layer is determined by a first set ofreception parameter, and wherein an operation mode of the secondreception protocol layer is determined by a second set of receptionparameters, the method including the steps of:

-   -   storing a plurality of sets of reception parameters, each set of        reception parameters corresponding to a set of transmission        parameters;    -   providing a transmission protocol information indicating the        pair of first and second set of transmission parameters used for        processing the information before transmitting the information;    -   selecting a pair consisting of the first set of reception        parameters and the second set of reception parameters        corresponding to the pair of the first and second set of        transmission parameters on the basis of the transmission        protocol information;    -   providing the pair of the first set of reception parameters and        the second set of reception parameters to the first reception        protocol layer and to the second reception protocol layer;    -   processing the received signal in accordance with the reception        protocol to obtain the information,        when the program runs on a computer.

The present invention is based on the finding, that an efficientcross-layer adaptation can be performed, when, depending on a channelproperty and an optimization goal, a plurality of sets of parameters,each set of parameters determining an operation mode of a particularcommunication layer, is jointly determined. Therefore, a jointadaptation of multiple layers can be performed to achieve theoptimization goal, comprising for example a maximization of a userperceived quality while efficiently using communication resources.

Since the inventive approach is directed to the optimization of anoperation of communication layers embedded within a protocol stack,inter-layer dependencies can explicitly be taken into account.

In accordance with the present invention, a storage element is providedfor storing (or providing) the first plurality of sets of parametersdefining different operation modes of a first communication layer of aplurality of communication layers, and for providing a second pluralityof sets of parameters defining different operation modes of the secondcommunication layer. In order to perform a cross-layer optimization, theinventive concept provides a selector for selecting the first set ofparameters from the first plurality of sets of parameters and forselecting the second set of parameters from the second plurality of setsof parameters. Since the first communication layer and the secondcommunication layer can freely be chosen in order to achieve anoptimization goal, for example a transmission quality at a currentchannel condition (i.e. a current bit error probability), a flexibleoptimization scheme can be performed, wherein inter-layer dependenciescan explicitly be taken into account.

Since the inventive selector is operative for selecting the first andsecond set of parameters defining the respective operation mode of therespective communication layer in dependence of the optimization goal, aconsiderable degree of freedom with respect to possible optimizationscenarios can be achieved. For example, starting from the optimizationgoal and the current channel condition, the selector may be operativefor deciding which communication layer are to be jointly optimized inorder to achieve the optimization goal.

For example, the first communication layer comprises the applicationlayer, and the second communication layer comprises a data link layerand a physical layer, as is depicted in FIG. 9. If, for example an imageinformation is to be transmitted, then the first communication layer maybe operative to encode the image information to achieve a certain datacompression associated with an allowable distortion describing adifference between a transmitted and a received information. Hence, thecompressed image information has an information rate which is a minimumachievable information rate with respect to the transmission of theimage information without exceeding the predetermined distortion value.In this case, the optimization goal is an optimization of a transmissionquality to transmit the information with the information data ratewithout exceeding the predetermined distortion value. To achieve thisoptimization goal, the inventive selector may jointly optimize theapplication layer and the link layer consisting of the data link layerand of the physical layer.

In order to transmit the compressed image information, the bitsrepresenting the information have to be encoded so that a certainchannel data rate associated with a certain bit error probability,ideally supporting the minimum information rate associated with thedistortion, is achieved. To do so, the inventive selector selects afirst set of parameters to be used by the application layer forencoding, i.e. source encoding, and selects the second set of parametersfor managing a physical transmission of the information through acommunication channel. The second set of parameters may, for example,comprise a subset of encoding parameters to be used for performing aforward error correction encoding scheme, for example a Reed-Solomonencoding or a convolutional encoding. Additionally, the second set ofparameters may comprise a subset of physical layer parametersdetermining a modulation scheme, for example a quadrature amplitudemodulation (QAM) or phase-shift keying (PSK).

However, a data frame provided by the physical layer for transmissionnot only comprises the information but also comprises information headerintroduced by every communication layer in order to establish thepreviously mentioned peer-to-peer communication. In other words, notonly the information to be transmitted by the application layer and thesubsequent encoding of the information determine the channel data rate.However, only a certain amount of information bits can be transmittedwithin the transmittable information frame. Moreover, each communicationlayer receives a processed information from a communication layerarranged above, performs a further processing, and passes the furtherprocess information to a following communication layer. In order toprocess the information in accordance with the protocol stack, certainagreements are to be made between the communication layers, for examplea maximum allowable length of a forwarded data frame. Since theinventive selector operates on the communication layers, theabove-indicated inter-layer dependencies can explicitly be taken intoaccount, so that the available communication resources (for example theavailable bandwidth) can be efficiently used.

It is a further advantage of the present invention, that the inventiveoptimization approach can be applied to achieving a plurality ofoptimization goals, since the parameters determining the operation modesof communication layers. In particular, the inventive concept can beapplied to cross-layer optimization in a multi-user transmissionscenario. In this case, the optimization goal is an optimization of atransmission quality per user. In order to achieve the optimizationgoal, each user stream can explicitly be taken into account. Forexample, the first set of parameters determining the operation mode ofthe first communication layer (for example application layer) can bechosen such that the first user information is compressed independentlyfrom a second user information. Moreover, the obtained user stream canefficiently be scheduled by selecting the second set of parametersdetermining the operation mode of the second communication layer, whichmay be a link layer as depicted in FIG. 9. Hence, the inventive jointoptimization of the application layer source rate selection and of theadaptive data link and the physical layer transmission scheduling independency of the channel property in a multi-user communication systemcan be achieved.

Moreover, even a scheduling of the information streams associated withthe first user can be performed within the application layer. Forexample, the information to be transmitted is a video or an audio streamrepresented by a media data. An application layer media data schedulingis a process of deciding which data segment within one session has to betransmitted at what time, while data link and physical layertransmission scheduling determines which user is allowed to use thechannel at a given time, frequency or code, and, which modulation andchannel encoding scheme is to be used for a user. The inventiveoptimization scheme considers the set of different transmission stateson the data link and physical layer (i.e. modulation scheme, channelcode rate, support of re-transmissions etc.) together with a distortionand source rate information, i.e. about media data from the applicationlayer. In order to achieve the optimization goal, i.e. an optimumtransmission strategy for each user and for each media data segment, theinventive selector may select the first set of parameters and the secondset of parameters, so that an optimum transmission strategy isdetermined.

The inventive apparatus (optimizer) considers for example a partition ofchannel resources among multiple users which may result in differentdata rates for each user. Furthermore, a selection of differentmodulation or channel coding schemes can be applied, which may result indifferent packet loss rates and data rates associated with each user. Inorder to efficiently manage the transmission, a selectivere-transmission of lossy frames together with a selective link layeracknowledgement can be formed. In order to manage the information to betransmitted, the information source rate (for example media source rate)can be selected. For individual user, an information about a signal tonoise ratio (SNR) may be provided. Furthermore, even a relativeimportance of the information packet (media packet) may be taken intoaccount, which results from inter-packet dependencies such as in modernvideo compression schemes (MPEG, H.26x). The relative importance isdetermined by the influence of a lost media frame on the overallreconstruction quality at the receiver when using a decoding scheme forthe decompression.

The inventive apparatus may further consider a data rate information interms of a packet size for selected information data units (i.e. mediadata units). Moreover, even a retransmission of important media data canbe obtained by appropriately controlling an operation mode of theapplication thereby selecting the first set of parameters.

In accordance with the present invention, the optimum transmissionstrategy can be achieved by optimization of an objective function, whichcan be a cost function. The objective function can express, forinstance, a maximization of the user perceived quality of a userexperiencing the worst channel conditions among the users sharing thesame communication resources, for example the same communicationchannel.

A further advantage of the inventive concept is a better utilization ofcommunication resources, for example wireless network resources, whencompared to other prior art approaches. Moreover, the inventive approachallows supporting of more simultaneous users in the same system sincethe available communication resources are efficiently exploited. In thecase of the same number of users, an improved transmission quality peruser can be achieved. Moreover, the user perceived quality can moreequally be distributed among multiple users. Additionally, the presentinvention provides a concept for a dynamic adaptation of thecommunication system by optimization of the operation modes of thecommunication layers in order to take varying transmissioncharacteristics and application requirements at the same time intoaccount.

An optimization scheme used for optimization of a communication systemusing communication layers (protocol layers), i.e. B3G systems, iscross-layer design. Here several layers of the protocol stack spanningfrom application parameters to physical transmission are considered.FIG. 10 shows an embodiment of a communication system, where anoptimization of the communication system on the basis of cross-layeroptimization in a vertical manner for one specific application isdemonstrated.

The system shown in FIG. 10 comprises a sender 1001 (base station) and areceiver 1003. The sender 1001 applies a protocol stack 1005 forprocessing the application (information) to be transmitted. The protocolstack 1005 comprises an application layer, a transport layer, a networklayer, and a link layer, comprising, for example, a medium accesscontrol layer (MAC) and a physical layer (PHY). Accordingly, thereceiver 1003 applies a protocol stack 1007 for processing a receivesignal being a version of a transmit signal transmitted by the sender1001. The protocol stack 1007 (the receive protocol stack) comprises,accordingly, a link layer, an IP layer (corresponding to the networklayer), a TCP/UDP layer (corresponding to the transport layer), and anapplication layer.

FIG. 10 also demonstrates a peer-to-peer communication principle, wherethe corresponding layers, for example the transport layers and theTCP/UDP layer communicate with each other.

In order to optimize the system for the specific application, a bottomup information delivery is performed. For example, the link layerextracts a channel property as a physical restriction parameter, forexample a signal to noise ratio (SNR) or a maximum possible transmitpower. The physical restriction parameters are then transported to theapplication layer, where video streaming using real-time coding- andencoding schemes (codec) is performed. In other words, the applicationlayer adapts the real-time codec to the physical restriction parametersso that the required transmission quality for video streaming can beachieved.

Accordingly, the application layer may inform the link layer aboutquality of service (QOS) requirements (for example a certain bit errorprobability associated with a certain service). In this case, the linklayer may apply a more comprehensive encoding scheme so that the qualityof service requirement is fulfilled.

The cross-layer adaptation technique is based on inter-layer informationexchange across the traditional layers of the protocol stack to adaptthe system parts to a dynamically changing environment. As mentionedabove, the information travels in both directions, up and down theprotocol stack. Cross-layer information exchange means, that theapplication receives information from lower layers (for example the linklayer) about the current network conditions and predictable eventsinfluencing the transmission quality, i.e. handover. Accordingly, thelower layers may receive information about the current transmissionrequirements of the application, as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the present invention are described in detailwith respect to the following figures, in which:

FIG. 1 shows a block diagram of an inventive apparatus for controllingan operation of a plurality of communication layers in accordance with afirst embodiment of the present invention;

FIG. 2 shows a block diagram of an inventive apparatus for controllingan operation of a plurality of communication layers in accordance with afurther embodiment of the present invention;

FIG. 3 shows a block diagram of an inventive apparatus for controllingan operation of a plurality of communication layers in accordance with afurther embodiment of the present invention;

FIG. 4 demonstrates control frame scheduling;

FIG. 5 a demonstrates an importance of transmitted frames;

FIG. 5 b demonstrates a performance of the inventive apparatus forcontrolling an operation of a plurality of communication layers;

FIG. 6 demonstrates transmission time arrangements in a multi-userscheduling approach;

FIG. 7 demonstrates the inventive scheduling approach for multiple usersin accordance with the present invention;

FIG. 8 demonstrates a performance of the inventive apparatus forcontrolling an operation of a plurality of communication layers withrespect to a maximization of a transmission quality of a worstperforming user;

FIG. 9 shows a protocol stack;

FIG. 10 shows a cross-layer design principle;

FIG. 11 a shows a multi-user scheduling with different timearrangements;

FIG. 11 b shows a size (in terms of packets) for a group of pictures in3 measured videos;

FIG. 12 shows a block diagram of a considered communication system;

FIG. 13 shows an inventive system architecture for joint layeroptimization;

FIG. 14 shows a MSE for a group of pictures in 3 measured videos;

FIG. 15 shows a frame error rate with respect to signal-to-noise ratio;

FIG. 16 shows a performance comparison for scenario 1;

FIG. 17 shows performance comparison for scenario 2;

FIG. 18 shows performance comparison for scenario 3; and

FIG. 19 shows a performance improvement comparison of the 3 investigatedscenarios.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an apparatus for controlling an operation of a plurality ofcommunication layers in accordance with a first embodiment of thepresent invention.

The apparatus shown in FIG. 1 comprises a plurality of communicationlayers of a communication protocol stack 101, wherein a firstcommunication layer 103 and a second communication layer 105 areexplicitly depicted. The apparatus further comprises means 107 forproviding a property of a communication channel, wherein the means 107for providing the property has an input 109 and an output 111. The means107 for providing the property is coupled to the second communicationlayer 105 via the input 109. The output 111 of the means 107 forproviding the property is coupled to a selector 113 having a furtherinput 115 and an output 117. The output 117 of the selector 113 iscoupled to a storage element 119. The storage element 119 has an output121 coupled to a means 123 for providing a first parameter set and asecond parameter set to the first and second communication layer. Themeans 123 for providing the first and second parameter set has a firstoutput 125 coupled to the first communication layer 103, and a secondoutput 107 coupled to the second communication layer 105.

The apparatus shown in FIG. 1 is operative for controlling an operationof the plurality of communication layers comprised by the protocol stack101 in a layered communication system. The layered communication systemis operative for transmitting information through a communicationchannel to a remote communication system. As mentioned above, anoperation of the first communication layer 103 of the plurality ofcommunication layers is determined by the first set of parameters and anoperation of the second communication layer 105 of the plurality ofcommunication layers is determined by the second set of parameters. Thefirst set of parameters and the second set of parameters are provided bythe means 103 for providing the first and second set of parameters inorder to control the operation of the communication protocol stack independence of a channel property and of an optimization goal.

In order to perform an adaptation, the storage element 119 comprises afirst plurality of sets of parameters defining different operation modesof the first communication layer, and a second plurality of sets ofparameters defining different operation modes of the secondcommunication layer. The inventive selector 113 is coupled to thestorage element 119 for selecting the first set of parameters from thefirst plurality of sets of parameters and for selecting the second setof parameters from the second plurality of sets of parameters. Inparticular, the selector 119 is operative for selecting the first set ofparameters and for selecting the second set of parameters in dependenceof the channel property provided by the means 107 for providing theproperty and in dependence of an optimization goal provided via theinput 115 to the selector 113.

In order to control the operation of the plurality of communicationlayers, the means 103 for providing the first and second set ofparameters receives the first and second set of parameters from thestorage element 119, wherein the first and second set of parameters areselected by the selector 113 in order to achieve the optimization goal.

The second communication layer 105 may be operative for managing atransmission of the information through the communication channel. To doso, the second communication layer 105 may comprise a physical layerbeing further operative for extracting the property of the communicationchannel. The property of the communication channel may be a bit errorprobability, a signal to noise ratio (SNR), a available channel datarate associated with a certain bit error probability, a transmissiondelay, a transmission power associated with a bit error probability, achannel coherence time or a channel coherence bandwidth or a combinationthereof. In order to provide the channel property to the selector, themeans 107 for providing the property is coupled to the secondcommunication layer 105 for receiving the property of the communicationchannel. As mentioned above, the second communication layer 105 maycomprise a physical layer, to which the means 107 for providing theproperty is coupled. In order to receive the channel property from thephysical layer, the means 107 for providing the property may furthercomprise a protocol interface for interfacing with the physical layer.

As mentioned above, the selector 113 is operative for selecting thefirst set of parameters and the second set of parameters. Preferably,the selector 113 is operative for jointly selecting the first and secondset of parameters as a pair of parameters in order to simultaneouslycontrol an operation mode of the first and of the second communicationlayer. In other words, the selector 113 jointly selects the first andthe second set of parameters, so that the optimization goal provided viathe input 115 can be achieved, wherein the inter-layer dependencies areexplicitly taken into consideration.

For example, the storage element 119 may be operative for storing or,generally, for providing the first and second plurality of sets ofparameters, from which the first set of parameters and the second set ofparameters can jointly be selected, so that the inter-layer dependencyis taken into account.

Generally, the first set of parameters may comprise a plurality of setsof parameters for controlling the whole operation mode of the firstcommunication layer 103. Accordingly, the second set of parametersselectable by the selector 113 may comprise a plurality of sub-sets ofparameters, wherein each sub-set of parameters of the second set ofparameters determines a certain sub-operation mode of the secondcommunication layer. By the way of example, the second communicationlayer 105 may comprise the data link layer and the physical layer, asdepicted in FIG. 9. In this case, the second set of parameters maycomprise a data link layer sub-set of parameters for controlling theoperation mode of the data link layer, and a physical layer sub-set ofparameters for controlling an operation mode (sub-operation) of thephysical layer. In this way, scheduling (which is a certain form ofencoding) and a further encoding, i.e. by applying a forward errorcorrection encoding scheme, can be determined.

Simultaneously, the sub-operation mode of the physical layer can becontrolled by the physical layer sub-set of parameters. For example, thephysical layer sub-set of parameters determines a modulation schemeapplied to modulation of the data frame prior to transmission.Simultaneously, the first set of parameters determines the operationmode of the first communication layer 103 which can be, for example, theabove-discussed application layer. In this case, the first set ofparameters controls a data compression encoding scheme associated with acertain rate distortion characteristic. Since the first set ofparameters and the second set of parameters are jointly selected forcontrolling the operation mode of the first and of the secondcommunication layer, a global optimization with respect to theoptimization goal and to the current channel condition can be achieved,so that all available, controllable, communication resources can jointlybe optimized.

As mentioned-above, the storage element 119 is operative for storing thefirst and the second plurality of sets of parameters defining differentoperation modes of the first and of the second communication layer. Forexample, the first plurality of sets of parameters and the secondplurality of sets of parameters are pre-computed, for example byoptimization over a plurality of scenarios, wherein the optimization maybe performed by an external computer entity. In other words, the storageelement 119 may comprise jointly optimized sets of parameters to be usedin different scenarios. An advantage of this approach is, that anadaptation of the protocol stack can be performed dynamically, i.e.during a transmission operation. A further advantage of this approachis, that the adaptation process may be performed quickly, since,depending on the channel property and on the optimization goal, theselector 113 may directly select the actually optimized pair consistingof the first and second set of parameters.

FIG. 2 shows a block diagram of an apparatus for controlling anoperation of a plurality of communication layers in accordance with afurther embodiment of the present invention.

Unlike the apparatus shown in FIG. 1, the apparatus of FIG. 2 comprisesa selector 201 having, additionally, a first input 203 and a secondinput 205. The first communication layer 103 is coupled via the firstinput 203 to the selector 201. Accordingly, the second communicationlayer 105 is coupled via the second input 205 to the selector 201.

Additionally, the apparatus shown in FIG. 2 comprises a means 207 forproviding the optimization goal. The means 207 for providing theoptimization goal has an input 209 coupled to a plurality ofcommunication layers, as is indicated in FIG. 2. Furthermore, the means207 for providing the optimization goal comprises an output 211 coupledto a further input 209 of the selector 201.

The selector 201 is coupled to the first and to the second communicationlayers for monitoring a current status of the protocol stack 101. Inparticular, the selector 201 may comprise a decision element formonitoring a current status of the first communication layer, whereinthe current status of the first communication layer is determined by acurrent first set of parameters, i.e. the set of parameters currentlydetermining an operation mode of the first communication layer.Accordingly, the decision element of the selector 201 is operative formonitoring a current status of the second communication layer determinedby a current second set of parameters. Depending on the currentstatuses, the optimization goal and the channel property, the decisionelement may be further operative for generating a control informationindicating, whether the optimization goal can be achieved using thecurrent first and second set of parameters or whether the current firstset of parameters and the current second set of parameters should bereplaced. In particular, the control information provided by thedecision element may indicate, that the first set of parameters and/orthe second set of parameters are to be selected by the selector 201 inorder to achieve the optimization goal, when the optimization goalcannot be achieved by the current first and second set of parameters.

As indicated in FIG. 2, the means 207 for providing the optimizationgoal may be coupled to the plurality of communication layers forreceiving the optimization goal. The optimization goal may be, forexample, an application oriented optimization goal, for example acertain quality of service provided by the first communication layer,when the first communication layer is an application layer. In thiscase, the means 207 for providing the optimization goal is coupled tothe application layer for receiving the application orientedoptimization goal.

Accordingly, the optimization goal may comprise an optimization of aphysical transmission through the communication channel. In this case,the means 209 for providing the optimization goal is coupled to thesecond communication layer and is operative for managing the physicallayer transmission for the communication channel using, for example, adata link layer and a physical layer. In this case, the optimizationgoal may be, for example, an optimization of an exploitation of theavailable bandwidth. By, for example, channel encoding (for exampleconvolutional coding) etc. In this case, the means 207 for providing theoptimization goal receives the transmission-oriented optimization goaland provides the same to the selector 201. Accordingly, the optimizationgoal may be application- and transmission-oriented. In this case, themeans 207 for providing the optimization goal is coupled to the firstcommunication layer 103 and to the second communication layer 105 forobtaining an orientation-oriented part of the optimization goal and atransmission-oriented part of the optimization goal.

In order to communicate with the physical layers, the means 207 forproviding the optimization goal may comprise a protocol layer interfacefor interfacing with the first communication layer and with the secondcommunication layer.

As mentioned above, the inventive approach may be applied to optimizingthe operation of the protocol stack in a multi-user scenario, where aplurality of users shares the same communication resources. To be morespecific, the information to be transmitted may comprise a firstinformation associated with a first user and a second informationassociated with a second user in the multi-user scenario. As mentionedabove, the optimization goal is in this case an optimized transmissionquality for a particular user, e.g. for the first information and forthe second information. For example, the optimization goal is totransmit the first information with a first information rate associatedwith a first distortion and to transmit the second information having asecond information rate associated with a second distortion through thecommunication channel and to determine a first channel data rateassociated with the first user stream and with a first bit errorprobability, so that the first information rate associated with thefirst distortion is supported. Accordingly, the goal is to transmit thesecond user stream via the communication channel with a second channeldata rate without exceeding the bit error probability, so that thesecond information rate associated with the second distortion issupported. Generally, the first communication layer may be operative forencoding the first information to obtain a first information signalassociated with the first user and a second information signalassociated with the second user, wherein the first information signalmay have the first information rate and the second information signalmay have the second information rate. In order to transmit theinformation through the communication channel, the second communicationlayer may be operative for encoding the first information signal and thesecond information signal to obtain a composite signal to be transmittedthrough the communication channel.

In this case, the inventive selector is operative for jointly selectingthe first set of parameters to be used by the first communication layerfor encoding the first information and the second information to obtainthe first information signal and the second information signal, and toselect the second set of parameters to be used by the secondcommunication layer for encoding the first information signal and thesecond information signal to provide the composite signal to betransmitted through the communication channel, wherein the firstcommunication layer and the second communication layer use the jointlyselected first set of parameters and the second set of parameters tooptimize the transmission quality of the first information and thetransmission quality of the second information.

For example, the second communication layer is operative for schedulingthe first information signal and the second information signal, so thatthe first information signal is transmitted within a first time frameand the second information signal is transmitted within a second timeframe. The scheduling has an impact of a resulting channel data rate ofthe corresponding scheduled information signal, or, generally,information stream. The first selector is then operative for selectingthe first set of parameters to obtain the first information signalhaving the first information rate associated with the first distortionand to obtain the second information signal having the secondinformation rate associated with the second distortion and for selectingthe second set of parameters to obtain the composite signal having adata rate supporting the first information rate and the secondinformation rate. The information rate may be for example a number ofinformation packets per time unit, for example a number of informationbits per second representing the respective information.

Moreover, the inventive approach may be also applied for informationscheduling, for example media data scheduling described above.

Since the selector is operative for controlling the whole operation ofthe protocol stack by selecting appropriate sets of parameters, theinventive approach may be also applied to both: information data ormedia data scheduling and user scheduling. For example, the firstinformation associated with the first user comprises a firstsub-information and a second sub-information, for example an audio- anda video signal. The inventive selector is then operative for selectingthe first set of parameters to be used by the first communication layerfor selectively encoding the first sub-information and the secondsub-information to obtain the first information signal comprising theencoded first and second sub-information, having, for example, differentinformation rates associated with different distortion profiles.Furthermore, the selector may be operative for selecting the first setof parameters for scheduling the first sub-information within the firstinformation signal and for scheduling the second sub-information withinthe first information signal, so that the first sub-information and thesecond sub-information are placed at different positions of the firstinformation signal. In other words, a decision is made which datasegment has to be transmitted within one session.

In accordance with the present invention, the inventive apparatus forcontrolling the operation of a plurality of communication layers mayfurther comprise means for determining the first communication layer andthe second communication layer from the plurality of communicationlayers to achieve the optimization goal. The means for determining thefirst communication layer and the second communication layer isoperative for making a decision which communication layers of theplurality of communication layers have to be optimized in order toachieve the optimization goal. The means for determining determines thefirst communication layer of which the first set of parameters is to beselected and the second communication layer of which the second set ofparameters is to be selected for achieving the optimization goal.

According to a further embodiment of the present invention, theinventive apparatus for controlling the operation of a plurality ofcommunication layers may be operative for user scheduling and schedulingof information associated with each user, as described above. Forexample, the optimization goal comprises an optimization of thetransmission quality in the multi-user scenario. The information maycomprise a first information associated with a first user and a secondinformation associated with the first user, a third informationassociated with a second user and a fourth information associated withthe second user. Generally, the inventive approach can be used in thecase of a plurality of informations and/or in the case of a plurality ofusers. The first communication layer is operative for scheduling thefirst information and the second information to obtain a firstinformation signal comprising the scheduled first and second informationassociated with the first user. Accordingly, the first communicationlayer is operative for scheduling the third information and the fourthinformation to obtain a second information signal associated with thesecond user. Accordingly, the second communication layer is operativefor scheduling the first information signal and the second informationsignal to obtain a scheduled multi-user stream. In order to achieve theoptimization goal mentioned-above, the inventive selector is operativefor jointly selecting the first set of parameters to be used by thefirst communication layer to provide the first information signal andthe second information signal, and the second set of parameters to beused by the second communication layer to provide the scheduledmulti-user stream to be transmitted via the communication channel.

FIG. 3 shows an apparatus for controlling an operation of a plurality ofcommunication layers in the case of multi-user and multi-mediascheduling.

The apparatus shown in FIG. 3 comprises a cross-layer optimizer 301,which is an application oriented optimizer. The cross-layer optimizerhas a first input 303, a second input 305 and an output 307.Additionally, the apparatus shown in FIG. 3 comprises a first interface309 having an input 311 and an output coupled to the input 303 of thecross-layer optimizer (X-layer optimizer). Additionally, the apparatuscomprises a second interface 313 having an input 315 and an outputcoupled to the second input 305 of the cross-layer optimizer. The firstinterface 309 is coupled via the input 311 to the application layer ofthe protocol stack 1005 previously discussed. Accordingly, the secondinterface 313 is coupled via the input 315 to the link layer of theprotocol stack 1005.

The apparatus shown in FIG. 3 further comprises a decision element 317having an input, a first output and a second output. The output 307 ofthe cross-layer optimizer 301 is coupled to the input of the decisionelement 317. The first output of the decision element 317 is coupled tothe application layer of the protocol stack 1005, and the second outputof the decision element 317 is coupled to the link layer of the protocolstack 1005.

In accordance with the present invention, a cross-layer optimizationapproach for wireless media transmission is provided. In particular, ajoint optimization of media data scheduling and multi-user schedulingcan be achieved, since the application layer and the link layer arejointly optimized. The motivation for the inventive cross-layer designare the mobile communication challenges like for example a dynamicbehavior of the communication system being characterized by a(non-predictable) variation of quality and diversity of connectivity.Additionally, certain dynamic requirements with respect to transmittedservices and applications have to be made with respect to significantdifferences in requirements (e.g. quality of service), changingrequirements as of user preferences, and short technology evolutioncycles requiring system's flexibility.

Contrary to the traditional layered systems, where a protocolintercommunication is strictly defined which results in an inefficientuse of resources, since each protocol is optimized for worse conditionindependently, the inventive approach as demonstrated in FIG. 3 providesa possibility of a global optimization of a behavior of the protocolstack by jointly optimizing a plurality of protocol layers.

As shown in FIG. 3, an information about a multi-media scheduling (e.g.source rate scheduling) is provided via the first interface 309 to thecross-layer optimizer 301. Accordingly, the second interface 303provides a multi-user scheduling information, e.g. transmit ratescheduling to the cross-layer optimizer 301, so that a (new) first setof parameters can be provided to the application layer and a (new)second set of parameters can be provided to the link layer, so that anoptimum multi-media scheduling and multi-user scheduling can beprovided, so that the communication resources are effectively exploited.

The cross-layer optimizer 301 corresponds to the inventive selectorbeing operative for selecting the first and second set of parameters.The decision element 307 decides, which set of parameters is to beprovided to which protocol layer.

In the following and by the way of example only, as an implementationembodiment, a video streaming server residing in the base station andmobile devices hosting streaming clients will be considered,respectively. The optimization goal is to maximize the end-to-endquality perceived by the users, while efficiently using the wiresresources. Video data scheduling is the process of deciding which datasegment in one streaming session has to be transmitted at what time,while multi-user scheduling, which belongs to data link layerscheduling, determines for instance which user is allowed to use thechannel at a given time, frequency or code.

In the following, the main features of streaming video that are relevantin the considered scenario will be discussed. The video is pre-encodedat multiple bit rates using a standard video compression scheme and thecorresponding video streams are stored on the streaming server. When thevideo stream is requested by the client, the video stream is packetizedand sent to the receiver. The receiver pre-buffers some data beforeplayout begins which allows a smoothing of some of the transmissionquality variations. The end-to-end latency of the application isdirectly related to the amount of data that is stored prior to playout.The number of bits to be sent for each video frame depend on what kindof encoding mode is selected.

In reference to FIG. 4, so-called I-frames being encoded withoutreference to previous frames and P-frames that are encoded by forming aprediction from previous frames can be distinguished. While I-frames canbe decoded without receiving the previous frame, the P-frames typicallycannot be decoded without this side-information. As a result, theI-frames are bigger than P-frames, as depicted in FIG. 4.

In order to allow fast forward and interactive scene selection, I-framesare typically introduced about every 500 to 1000 ms. An I-frame and allthe following P-frames up to the end excluding the next I-frame will bereferred to in the following as a group of pictures (GOP). In order toprovide the I-frames and the P-frames, a control frame scheduling isperformed to determine a frame priority. The source parameters may be asource rate, a number of frames per second, a delay constraint, and adistortion profile of a group of pictures.

In the following it is assumed, that the reconstruction quality at thereceiver depends on the number of successfully decoded frames within agroup of pictures. Since a successful decoding of P-frames depends on anerror-free reception of all previous frames of the same group ofpictures, loosing the first frame of a group of pictures leads to theworst result. In this case, the most recent decoded frame is displayedas a still image until the next I-frame is successfully received.Loosing the last frame of a GOP leads to little distortion as just thesecond last frame of the GOP is displayed twice.

FIG. 5 a shows a simulation result in terms of the mean squared error(MSE), which is the mean squared reconstruction error in this case for agroup of pictures consisting of 15 frames when loosing different framesfor three different videos. Additionally, three different scenarios,namely Carphone, Foreman and Mother-Daughter scenario are considered. Ascan be seen from FIG. 5 a, the MSE is at the largest, when loosing thefirst frame of a GOP. The distortion decreases as is proceeded withinthe GOP and becomes just the encoding distortion, which is a function ofthe bit rate of the video stream, when all frames are timely anderror-free received, which is referred to as index 16 in FIG. 5 a. Theactual error depends on the scene content. If there is little motion inthe sequence, the loss of a frame has little effect on the quality ofthe constructed sequence. If there is a significant motion, however, theinfluence of a lost frame can be significant.

In video data scheduling, the application has to decide when to send aframe, which is described in P. A. Chou, and Z. Miao “Rate-DistortionOptimization Streaming of Packetized Media”, Technical ReportMSR-TR-2001-35, Microsoft Research, Microsoft Corporation, February2001. As the first frame of GOP is the most important one, theapplication will increase the probability of error-free reception byassigning the most priority to this frame during scheduling. This meansfor instance, that the I-frame is transmitted twice while all otherframes of the GOP are transmitted only once. Depending on the availabletransmission rate, the application therefore can choose betweendifferent frame scheduling patterns by selecting different sets ofparameters.

In wireless networks, each base station serves multiple users (clients)or mobile stations by means of time-division, frequency-division orcode-division. Multi-user scheduling, which is a part of data link layerscheduling, determines which user is allowed to use the channel at apredetermined time, frequency or code. By scheduling the multi-usertransmission based on user demand and channel stage, the efficiency ofutilizing the resource can be improved significantly. In particular,each user might obtain different transmission data rates, when differentscheduling or arrangements of the transmission is performed.

FIG. 5 b shows selected experimental results demonstrating theperformance of the inventive cross-layer information exchange. In theexperiments shown in FIG. 5 b, three users with three different videosare optimized for a case of seven different scheduling scenarios shownin FIG. 6. In particular, FIG. 6 shows an example with three users,which are arranged with seven different cases of transmission time. Oneof these cases is chosen for providing the experimental results for thedata link layer by maximizing the end-to-end quality perceived by theusers, which is a part of the task of the inventive cross-layeroptimizer. Each case applies an optimized frame scheduling pattern forthe resulting transmission data rate.

Referring again to FIG. 5 b, one case out of the seven cases is chosenfor maximizing the minimum performance among the three users. Inparticular, FIG. 5 b shows a peak signal to noise ratio (PSNR)improvement of the worst user in the selected case compared to that incase 1 of FIG. 6, which can be considered as performance withoutcross-layer optimizer. As can be seen, a probability of an improvementlarger than 1 dB is more than 40%.

In accordance with the present invention, the transmission parametersmay be a data rate and an error rate for the link layer, a distance interms of the signal to noise ratio (SNR), a speed in terms of channelcoherency time and a modulation scheme in the physical layer. The linklayer is operative for scheduling the system resources for multipleusers as depicted in FIG. 7.

FIG. 8 shows a further experimental result with respect to amaximization of transmission quality of the worst performing user.

In FIG. 8 a cumulative density probability function (CDPF) versus ΔPSNRcompared to the case number 1 is shown, demonstrating the performance ofthe inventive approach. The upper-right diagram shown in FIG. 8demonstrates the system performance in terms of a frequency of thetransmission of a selected case 1-7.

In accordance with a further aspect of the present invention, acommunication apparatus for processing an information to be transmittedin accordance with a transmission protocol is provided. The transmissionprotocol may comprise a plurality of protocol layers as described above.The inventive communication apparatus comprises an information sourcefor providing the information and the apparatus for controlling theplurality of protocol layers in accordance with the previousdescriptions. In order to process the information in accordance with thetransmission protocol, the inventive communication apparatus furthercomprises a processor for processing the information in accordance withthe protocol layers. The processor may be, for example, a networkprocessor.

Accordingly, the present invention further provides a communicationapparatus for processing a received signal in accordance with areception protocol, wherein the reception protocol is a protocolimplemented in the receiver. The received signal is a received versionof the transmit signal transmitted through a communication channel,wherein the transmit signal comprises an information processed inaccordance with a transmission protocol in a transmitter. Thetransmission protocol may comprise a first transmit protocol layer(first transmission protocol layer) and a second transmit protocol layer(second transmission protocol) as described above, wherein an operationmode of the first transmission protocol layer is determined by a firstset of transmit (transmission) parameters and wherein an operation modeof the second transmission protocol layer is determined by a second setof transmission parameters. As described above, the first set oftransmission parameters and the second set of transmission parametersmay be pair-wise selected from a plurality of transmission parameters independence on a property of the communication channel and, optionally,on an optimization goal, as described above. The receive protocolcomprises a first receive (reception) protocol layer and a secondreceive (reception) protocol layer, wherein an operation mode of thefirst receive protocol layer is determined by a first set of receive(reception) parameters, and wherein an operation mode of the secondreceive protocol layer is determined by a second set of receive(reception) parameters. The inventive apparatus comprises a storageelement for storing a plurality of sets of receive parameters, each setof receive parameters corresponding to a set of transmit parameters. Thestorage element corresponds to the inventive storage element describedabove. Furthermore, the apparatus may comprise means for extracting thefirst set of receive parameters and the second set of receive parametersfrom the first receive protocol layer and from the second receiveprotocol layer in accordance with the functionality described above.

The inventive apparatus may further comprise means for providing atransmit protocol information indicating the pair of the first and thesecond set of transmit parameters used for processing the informationbefore transmitting the information. In other words, the inventive meansfor providing the transmit protocol information indicates, whichoperation mode of which protocol layer is to be considered. Accordingly,the inventive apparatus comprises a selector for selecting a pairconsisting of the first set of receive parameters and the second set ofreceive parameters corresponding to the pair of the first and the secondset of transmit parameters on the basis of the transmit protocolinformation. Additionally, the inventive apparatus comprises means forproviding the pair of the first set of receive parameters and the secondset of receive parameters to the first receive protocol layer and to thesecond receive protocol layer. The functionality of the means forproviding the pair of the first set of receive parameters and of thesecond set of receive parameters may be identical to that describedabove in connection with a means for providing the first and the secondset of parameters to the first and second communication layer.

Additionally, the inventive apparatus for processing the received signalcomprises a processor for processing the received signal in accordancewith the received protocol to obtain the information.

Furthermore, the inventive apparatus may comprise a controller forproviding a signaling information to the selector, wherein the signalinginformation indicates whether the pair consisting of the first andsecond set of parameters is to be selected. Furthermore, the inventivecontroller is operative for generating the signaling information fromthe transmit protocol information and a received protocol informationindicating a pair of the first and second set of received parameterscurrently used by the receive protocol.

To provide the receive protocol information, the inventive apparatusfurther comprises means for extracting the first set of receivedparameters from the first received protocol layer and the second set ofreceived parameters from the second received protocol layer in order tomonitor a current status of protocol layer.

The provided apparatus and methods may be used to optimize atransmission of media data in wireless communication by inter-layerinformation exchange. The inventive optimization is enabled by jointedoptimization of media data scheduling on the application layer andmulti-user scheduling on the link layer. Therefore, an end-to-endquality perceived by the users is improved by efficiently using thewireless resources. Moreover, the inventive approach can be of benefitin service provisioning systems for wireless networks in order toovercome the highly dynamic characteristics of transmission capabilitiesand application requirements.

It is to be noted that the inventive approach can generally be used inthe case of a plurality of users and/or in the case of a plurality ofinformations associated to each user.

As mentioned above, the sets of parameters may be jointly pre-computed,so that the inventive selector selects actually optimized sets ofparameters.

In the following, we describe cross-layer optimization of applicationlayer and radio link layer for wireless multi-user multimediacommunication. Our aim is to optimize the end-to-end quality of thewireless media application as well as efficiently utilize the wirelessresources. A new architecture for achieving our goal is provided andformulated. This architecture consists of the process of parameterabstraction, a cross-layer optimizer, and the process of decisiondistribution. In addition, sample numerical results are provided toreveal the potential of the inventive joint optimization. Cross layerdesign in mobile communication has recently gained much attention in thecontext of multimedia service provisioning (e.g., voice, video, audio,data). The concept of cross-layer design introduces inter-layer conceptsacross the protocol stack and allows us to jointly optimize thecommunication on two or more layers. Although this concept can beemployed in all communication networks, it is especially important inwireless networks because of the unique challenge of the wirelessenvironment (i.e., the time-varying and the fading nature of thewireless channels). This wireless nature and user mobility lead torandom variation in network performance and connectivity. In addition,the demanding quality of service (QoS) requirements (e.g., data rate,latency, continuity and error rate) for multimedia support makes mobilemultimedia communication even more challenging in system design. Thischallenge will be hard to meet with a conventional layered designapproach, which separates system design into essentially independentlayers. In order to provide end-to-end QoS, parameter adaptation has tobe addressed at all OSI (Open Systems Interconnection) layers.Therefore, the inventive concept of cross-layer design is provided, forwhich information has to be exchanged between different layers. In thefollowing, we exploit the inter-layer coupling of a cross layer designconcept by proposing a joint application and radio link layeroptimization for wireless multimedia communication. We refer to theradio link layer as the physical layer and the data link layer in theprotocol stack. Our aim is to optimize the end-to-end quality of thewireless multimedia communication application as well as efficientlyutilize the wireless resources. To achieve this aim, an architecture forthe joint layer optimization is developed to provide a potentialsolution for the implementation of the cross layer optimization concept.This architecture consists of the process of parameter abstraction,across-layer optimizer, and the process of decision distribution. Everypart in this architecture is formalized. In addition, sample numericalresults are provided to reveal the potential of the inventive jointoptimization. Previous work mainly concentrates on optimizing theperformance at a single layer, such as the adaptation of the applicationto the transport, network, data-link and physical layer characteristics(bottom-up approach) and the adaptation of the physical, data link ornetwork layers to the application requirements (top-down approach). Mostof the on-going research in cross layer design focuses on jointoptimization of the physical layer and data link (or MAC) layer. Someinclude the optimization of routing at the network layer in the crosslayer optimization for ad hoc wireless networks and others include thesource rate in the joint optimization of transmit power and forwarderror correction coding at the physical layer.

The present approach is different from previous approaches in that ourgoal is preferably to optimize the end-to-end quality of multimediaapplications. For this we consider the joint optimization of threelayers in the protocol stack, namely the application layer (layer 7),the data link layer (layer 2), and the physical layer (layer 1). Weinclude the application layer in the joint optimization because theend-to-end quality observed by the users directly depends on theapplication and the application layer has direct information about theimpact of each successfully decoded piece of media data on the perceivedquality. We also include the physical layer and the data link layer inour consideration because the unique challenge of mobile wirelesscommunication results from the nature of the wireless channel, whichthese two layers have to cope with. A new architecture for achieving ourgoal is provided and formulated. The structure of this paper is asfollows.

We assume streaming video as an example application for the multimediaservice and consider a video-streaming server located at the basestation and multiple streaming clients located in mobile devices. Asshown in FIG. 12, K streaming clients or users are assumed sharing thesame air interface and network resources but requesting different videocontents. Note that only the protocol stack necessary for the wirelessconnection has to be considered since in our scenario the videostreaming server is located directly at the base station. Therefore, thetransport layer and the network layer in the protocol stack can beexcluded from our optimization problem. We focus on the interactionbetween the application layer and the radio link layer, whichincorporates both the physical (PHY) layer and the data link layer. Atthe base station, an architecture as shown in FIG. 13 is suitable toprovide end-to-end quality of service optimization. This Fig.illustrates the tasks and information flows related to the jointoptimization. Necessary state information is first collected from theapplication layer and the radio link layer through the process ofparameter abstraction for the cross-layer optimizer. The process ofparameter abstraction results in the transformation of layer specificparameters into parameters that are comprehensible for the cross-layeroptimizer, so called cross-layer parameters. Then, the optimization iscarried out by the cross-layer optimizer with respect to a particularobjective function. From a given set of possible cross-layer parametertuples, the tuple optimizing the objective function is selected. Afterthe decision on a particular cross-layer parameter tuple is made, theoptimizer distributes the decision information back to the correspondinglayers. Note that the set of possible cross-layer parameter tuples ingeneral can be infinite. It is necessary to pre-select only a finite setof appropriate tuples in order to obtain the decision quickly. In thisway, the final decision on the optimal cross-layer parameter tuple mightresult only in a local optimum.

In order to carry out the joint optimization, state information or a setof key parameters have to be abstracted from the selected layers andprovided to the cross-layer optimizer. This is necessary because layerspecific parameters may be incomprehensible or of limited use to otherlayers and the optimizer.

In wireless networks, the physical layer and the data link layer arededicatedly designed for the dynamic variation of the wireless channelduring the provision of a particular service. This is in contrast towireline networks which experience much less dynamic variation. Thephysical layer deals with the issues including transmit power (throughtransmit power control), channel estimation, synchronization, signalshaping, modulation and signal detection (through signal processing),while the data link layer is responsible for radio resource allocation(multi-user scheduling or queuing) and error control (by channel coding,usually a combination of forward error correction coding (FEC) andautomatic retransmission (ARQ)). Since both of these two layers areclosely related to the unique characteristics of the wireless nature, itis useful to consider them together. In the following, we refer to theircombination as the radio link layer. Since there are many issues in theradio link layer and these issues are related to each other, parameterabstraction is necessary. To be more specific, we define the setR={r₁,r₂, . . . } tuples r_(i)=(r_(i) ¹,r_(i) ², . . . ) of radio linklayer specific parameters r_(i) ^(j) (e.g., modulation alphabets, coderate, air time, transmit power, coherence time). Since these radio linkspecific parameters may be variable, the set R contains all possiblecombinations oft heir values and each tuple r_(i) represents onepossible combination.

In order to formalize the process of parameter abstraction, we definethe set {tilde over (R)}={{tilde over (r)}₁, {tilde over (r)}₂, . . . }of tuples {tilde over (r)}_(i)=({tilde over (r)}_(i) ¹,{tilde over(r)}_(i) ², . . . ) of abstracted parameters {tilde over (r)}_(i) ^(j).The relationship between the set R and the set {tilde over (R)} isestablished by the relationG⊂R×{tilde over (R)}with domain R and co-domain {tilde over (R)}, which realizes a mappingbetween R and {tilde over (R)}. Here, the symbol × refers to theCartesian product. G is the subset that defines the mapping between Rand {tilde over (R)}. We call this mapping process radio link layerparameter abstraction. For a single user scenario, for example, four keyparameters can be abstracted. They are transmission data rate d,transmission packet error rate e, data packet size s, and the channelcoherence time t. This leads to the abstracted parameter tuple {tildeover (r)}_(i)=(d_(i),e_(i),s_(i),t_(i)). In a K user scenario, one canextend the parameter abstraction for each user. The parameter tuple{tilde over (r)}_(i) then contains 4K parameters, {tilde over(r)}_(i)=(d_(i) ⁽¹⁾,e_(i) ⁽¹⁾,s_(i) ⁽¹⁾,t_(i) ⁽¹⁾, . . . ,d_(i)^((K)),e_(i) ^((K)),s_(i) ^((K)),t_(i) ^((K))), in which a group of fourparameters belongs to one user.

The transmission data rate d is influenced by the modulation scheme, thechannel coding, and the multi-user scheduling. The transmission packeterror rate e is influenced by the transmit power, channel estimation,signal detection, the modulation scheme, the channel coding, the currentuser position, etc. The channel coherence time t of a user is related tothe user velocity and its surrounding environment, while the data packetsize s is normally defined by the wireless system standard. Theseinter-relationships define the relation G. Alternatively, it is possibleto transform the transmission packet error rate e and the channelcoherence time t into the two parameters of the two-stateGilbert-Elliott model, which are the transition probabilities (p and q )from one state to another. The transformation is given by

$p = {{\frac{es}{td}\mspace{14mu}{and}\mspace{14mu} q} = \frac{\left( {1 - e} \right)s}{td}}$where p is the transition probability from the good state to the badstate and q is the transition probability from the bad state to the goodstate.

In this way, the abstracted parameter tuple becomes {tilde over(r)}_(i)=(d_(i) ⁽¹⁾,p_(i) ⁽¹⁾,s_(i) ⁽¹⁾,q_(i) ⁽¹⁾, . . . ,d_(i)^((K)),p_(i) ^((K)),s_(i) ^((K)),q_(i) ^((K))) One advantage of thistransformation is that the resulting parameter tuple {tilde over(r)}_(i) is more comprehensible for high layers in the protocol stack.

The application layer is the layer where the media data is compressed,packetized, and scheduled for transmission. The key parameters to beabstracted for the cross-layer optimization are related to thecharacteristics of the compressed source data. This implies that thesekey parameters may depend on the type of application or service becausethe characteristics of the compressed source data may depend on theapplication or service. For a formal description, let us define the setA={a₁,a₂, . . . } of tuples ã_(i)=(ã_(i) ¹,ã_(i) ², . . . ) ofapplication layer specific parameters ã_(i) ^(j). Since theseapplication layer specific parameters may be variable, the set Acontains all possible combinations of their values and each tuplerepresents one possible combination. We further define the set Ã={ã₁,ã₂,. . . } of tuples ã_(i)=(ã_(i) ¹,ã_(i) ², . . . ) of abstractedparameters ã_(i) ^(j). The relationship between the set A and the set Ãis established by the relationH⊂A×Ã

with domain A and co-domain Ã, which realizes a mapping between A and Ã.We call this mapping process application layer parameter abstraction. Inthe following, we assume a streaming video service. The abstractedparameters of this service include the source data rate, the number offrames (or pictures) per second, size (in terms of bytes) and maximumdelay of each frame (or picture). Other important information for theoptimizer is the distortion-rate function (encoding distortion) and thedistortion profile of a particular lost frame(or picture) (see FIG. 14).FIG. 14 shows an example of the distortion profile of lost frames andthe encoding distortion for 3 different videos, each of which iscomposed of group of pictures(GOP) with 15 frames, which corresponds to0.5 seconds at a frame rate of 30 frames per second. The video sequenceare encoded at a mean data rate of 100 kbps. Each GOP starts with anindependently decodable intra-frame. The following 14 frames areinter-frames, which can only be successfully decoded if all previousframes of the same GOP are decoded error-free. The distortion isquantified by the mean squared reconstruction error (MSE), which ismeasured between the displayed and the original video sequence. Theindex in FIG. 14 indicates the loss of a particular frame. It is assumedthat as part of the error concealment strategy all following frames ofthe group of picture are not decodable and the most recent correctlydecoded frame is displayed instead of the non-decoded frames. Also, notethat the index 16 gives the MSE when all frames are received correctly,which we refer to as the encoding distortion because of the quantizationerror.

The abstracted parameter sets {tilde over (R)} and Ã) from both theapplication layer and the radio link layer form the input to thecross-layer optimizer. Since any combination of the abstracted parametertuples from the two input sets is valid, it is convenient to define thecross-layer parameter set{tilde over (X)}={tilde over (R)}×Ãwhich combines the two input sets into one input set for the optimizer.The set {tilde over (X)}={{tilde over (x)}₁,{tilde over (x)}₂, . . . }consists of tuples {tilde over (x)}_(n)=({tilde over (r)}_(i),ã_(j)) and|{tilde over (X)}|=|{tilde over (R)}|·|Ã|.

With the formalism introduced above, the operation of the cross-layeroptimizer Ω can now be described byΩ:{tilde over (X)}→{circumflex over (X)}⊂{tilde over (X)}

The optimizer selects from the input set {tilde over (X)} a truenon-empty subset {circumflex over (X)} that is the output of theoptimizer.

In the following, we assume |{circumflex over (X)}|=1, that is theoutput of the optimizer is a single tuple and {circumflex over(X)}={tilde over (x)}_(opt) ε {tilde over (X)}. The decision or outputof the cross-layer optimizer {tilde over (x)}_(opt) is made with respectto a particular objective functionΓ:{tilde over (X)}→Rwhere R is the set of real numbers. Therefore, the output of theoptimizer can be expressed as

${\overset{\sim}{x}}_{opt} = {\arg\mspace{11mu}{\min\limits_{\overset{\sim}{x} \in \overset{\sim}{X}}{\Gamma\left( \overset{\sim}{x} \right)}}}$

The choice of a particular objective function Γ depends on the goal ofthe system design and the output (or decision) of the optimizer might bedifferent for different objective functions. In the example applicationof streaming video, one possible objective function in a single userscenario is the MSE between the displayed and the original videosequence. For a multi-user situation, different extensions of the MSEare possible. For example, the objective function can be the sum of MSEof all the users. That is,

${\Gamma\left( \overset{\sim}{x} \right)} = {\sum\limits_{k = 1}^{K}{{MSE}_{k}\left( \overset{\sim}{x} \right)}}$where MSE_(k)({tilde over (x)}) is the MSE of user k for the cross-layerparameter tuple {tilde over (x)} ε {tilde over (X)}. This objectivefunction will optimize the average performance among all users. Othercommon definitions of the objective function include which optimizes theperformance of the worst performing user, and

${\Gamma\left( \overset{\sim}{x} \right)} = \mspace{11mu}{\max\limits_{{k = 1},\ldots\mspace{11mu},K}\mspace{11mu}{{MSE}_{k}\left( \overset{\sim}{x} \right)}}$which is equivalent to maximizing the sum of the peak-signal-to-noiseratio of all users.

Once the output (or decision) of the cross-layer optimizer {tilde over(x)}_(opt)=({tilde over (r)}_(opt), ã_(opt)) is obtained, the decisions{tilde over (r)}_(opt) and opt ã_(opt) have to be communicated back tothe radio link layer and the application layer, respectively. Duringthis, the process of parameter abstraction has to be reversed and theabstracted parameters {tilde over (r)}_(opt) and ã_(opt) are transformedback to the layer specific parameters r_(opt) ε R a_(opt) ε A. Thisreverse transformation is given byr_(opt) ε {r|(r,{tilde over (r)}_(opt)) ε G}anda_(opt) ε {a|(a,ã_(opt)) ε H}

In case the set {r|(r,{tilde over (r)}_(opt)) ε G} or the set{a|(a,ã_(opt)) ε H} has more than one element, the choice of aparticular element can be made at the corresponding layers individually.

In the following, we provide sample simulation results to evaluate theperformance of the inventive joint optimization. Throughout thissection, we assume 3 users (user 1, 2, and 3), each of which requests adifferent video. User 1, 2, and 3 request the Carphone (CP), Foreman(FM), and Mother-daughter (MD) video, respectively. We choose thepeak-signal-to-noise ratio (PSNR) as our performance measure. PSNR isdefined as PSNR=10 log₁₀(255²/MSE). The larger the PSNR is, the smallerthe MSE, which is computed between the original video sequence and thereconstructed sequence at the client or user. Therefore, the larger thePSNR is, the better the performance. As an example, we use the objectivefunction given above which maximizes the worst-case user's performance.

Therefore, the cross-layer optimizer chooses the parameter tuple thatminimizes the maximum of MSE (or equivalently maximizes the minimum ofthe PSNR)among the users. In the simulation, it is assumed that the datapacket size at the radio link layer is equal to 54 bytes, which is thesame as the specified packet size of the IEEE802.11a or HiperLAN2standard. The channel coherence time is assumed to be 50 ms for all thethree users, which approximately corresponds to a pedestrian speed (for5 GHz carrier frequency). Since the transmission data rate is influencedby the modulation scheme, the channel coding, and the multi-userscheduling, two different modulations (BPSK and QPSK) are assumed and itis further assumed that there are 7 cases of time arrangement in atime-division multiplexing based multi-user scheduling as shown in FIG.11 a. A user's transmission data rate is assumed to be equal to 100 kbpswhen BPSK is used and 2/9 of the total transmission time is assigned toit. Therefore, if QPSK is used and 4/9 of the total transmission time isassigned, the user can have a transmission data rate as high as 400kbps. The transmission error rate on the other hand depends on thetransmission data rate, the average SNR and the error correctingcapability of the channel code. Usually, the performance of a channelcode is evaluated in terms of the residual error rate (after channeldecoding) for a given receive SNR. In our simulation, we assume aconvolutional code of code rate ½ and a data packet size of 54 bytes.The residual packet error rate is shown in FIG. 15 as a function of SNR.However, in the wireless link, the receive SNR is not constant, butfluctuating around the mean value (long term SNR), which is due to fastfading caused by user mobility. In this way, the receive SNR can bemodeled as a random variable with a certain probability distribution,which is determined by the propagation property of the physical channel(e.g., Rayleigh distribution, Rice distribution). The residual packeterror rate in a fading wireless link is computed by averaging thispacket error ratio (e.g., from FIG. 15) with the fading statistics.Assuming Rayleigh fading, the resulting average packet error rate isgiven in FIG. 16 as a function of the average signal-to-noise ratio(SNR). This resulting average packet error rate is used as the parametere in our simulation. User position dependent path loss and shadowingcommonly observed in wireless links are taken into account by choosingthe long-term average signal-to-noise ratio randomly and independentlyfor each user uniformly within the range from 1 to 100 (0 dB to 20 dB).On the application layer, it is assumed that the video is encoded usingthe emerging H.264 video compression standard with 15 frames per GOP(per 0.5 second). Two different values of the source rate (100 kbps and200 kbps) are considered. This means that the video has been pre-encodedat two different target rates and both versions are stored on thestreaming server. We can switch from one source stream to the other atthe beginning of a GOP. In each GOP, the first frame is an I-frame andthe following 14 frames are P-frames. We use the measured distortionprofile of a particular lost frame and the encoding distortion for the 3requested videos. FIG. 14 shows an example of a distortion profile interms of MSE for a GOP at a source rate of 100 kbps. The MSE is measuredbetween the displayed and the original video sequence and averagedacross a GOP. In FIG. 14 , the index indicates the loss of a particularframe. It is assumed that all following frames of the GOP become notdecodable and the most recent correctly decoded frame is displayedinstead of the non-decoded frames. Note that the index 16 gives the MSEwhen all frames are received correctly, which is the encodingdistortion. Also, note that since successful decoding of P-framesdepends on error-free reception of all previous frames of the same GOP,losing the first frame of a GOP leads to the largest distortion, whilelosing the last frame of a GOP leads to little distortion. Furthermore,it is assumed that each video frame (or picture) is packetized withmaximum size of 54 bytes and each packet only contains data from oneframe. That is, each frame is packetized into an integer number ofpackets.

The size of each frame is determined during the encoding step. Thesevalues are stored along with the bit stream and the distortion profile.FIG. 11 b gives the size (in terms of packets) for a GOP in the threemeasured videos at a source rate of 100 kbps, where I and Pn (n=1, 2 . .. 14) denote the I-frame and the n-th P frame, respectively. We can seethat the size of an I-frame is much larger than that of a P-frame andthe size of a P-frame varies from frame to frame. This is related to thecontents of a video. Both, an operation mode without ARQ (referred to asForward Mode) and an operation mode with ARQ (referred to as ARQ Mode)are investigated. We consider every GOP as a unit and assume that eachGOP has to be transmitted within the duration of 0.5 second. In ForwardMode, we assume no acknowledgement from the clients is available and thevideo frames of every GOP for a particular client are repeatedlytransmitted when the transmission data rate is larger than the sourcedata rate. For instance, every GOP is transmitted twice if thetransmission data rate is twice as large as the source data rate. If thetransmission data rate is 1.5 times the source data rate, a GOP istransmitted once followed by retransmitting the I-frame, the firstP-frame, the second P-frame, etc., until the period of 0.5 second forthe GOP is expired. On the other hand, in ARQ Mode, we assume thatinstantaneous acknowledgement of a transmitted packet is available fromthe clients and the data packets of every GOP for a particular clientare retransmitted in the way that the data packets in a GOP are receivedsuccessfully in time order. That is, before transmitting anew packet, itis guaranteed that its previous packets in the GOP are receivedcorrectly. FIG. 17 to FIG. 19 provide simulation results of threescenarios (scenario 1, 2, and 3). In scenario 1, we restrict that onlyBPSK modulation is used at the radio link layer and only the source ratewith 100 kbps is available at the application layer. Therefore, only oneconstant abstracted parameter tuple (with 100 kbps for all 3 users) isprovided by the application layer in this scenario, while the radio linklayer provides 7 abstracted parameter tuples, which results from the 7cases of time arrangement shown in FIG. 11 a. The cross-layer optimizerselects one out of the 7 combinations of the input parameter tuples suchthat our objective function is optimized. The MSE is a random variablecontrolled by the two factors discussed above, namely fast fading anduser position dependent path loss and shadowing. In general, fast fadingtakes place in a much smaller timescale than the path loss andshadowing. In this paper, we evaluate the MSE averaged over fast fadingby taking the expected value of the MSE with respect to the fast fadingfor a particular position of the users or equivalently for a particularlong term SNR. Based on this value the cross-layer optimizer makes itsdecision. We also look at its statistical properties for an ensemble ofuser positions. Therefore, the cumulative density probability function(CDF) of this average MSE is chosen to show the performance of bothmodes (Forward Mode and ARQ Mode). The performance of the worstperforming user in the system with the inventive joint optimization(w/JO) is compared with that in a system without joint optimization (w/oJO). A system without joint optimization is assumed to assign the sameamount of transmission time to all the users (i.e., Case 1 in FIG. 11 a)and use BPSK modulation, while the source data rate is fixed to 100kbps. It can be seen from FIG. 17 that the PSNR of the worst performinguser improves significantly in the system w/JO. For instance, there isabout 1-40%=60% of the chance that the PSNR of the worst performing useris larger than 30 dB in the system w/JO in Forward Mode, which improves2 dB when compared to the system w/o JO. A similar trend of improvementcan be observed in FIG. 18 and FIG. 19 for scenario 2 and 3. In scenario2, the same abstracted parameter tuple as in scenario 1 is assumed atthe application layer but the radio link layer provides 14 abstractedparameter tuples, which result from the 7 cases of time arrangement withBPSK and another 7 cases of time arrangement with QPSK. The same systemwithout joint optimization (w/o JO) as described in FIG. 17 is alsoprovided for the purpose of comparison. In scenario 3, it is assumedthat the two different source rates of 100 kbps and 200 kbps for each ofthe 3 users are provided by the application layer (resulting in 2³=8parameter tuples). The same abstracted parameter tuples as in scenario 2are provided by the radio link layer. The performance improves when moreabstracted parameter tuples are provided because more degrees of freedomcan be obtained. This can be observed in FIG. 14 more clearly, where theperformance improvement of the investigated 3 scenarios is shown. Here,PSNR is defined as the difference between the PSNR of the worstperforming user in the system w/JO and that in the system w/o JO. Aclose observation of the left hand side FIG. in FIG. 14 reveals that theamount of performance improvement of scenario 2 is much larger than thatof scenario 1 in Forward Mode, while the amount of performanceimprovement of scenario 3 is only slightly larger than that of scenario2. This indicates that the choice of higher transmission data rate (byusing QPSK) provided by the radio link layer is favorable in thisapplication mode and the optimizer chooses it frequently. In contract,the choice of higher source rate (200 kbps) provided by the applicationlayer is not so favorable in this mode and the optimizer seldom choosesit. On the other hand, this choice of higher source rate is favorable inARQ Mode, which can be seen from the graph on the right hand side, wherethe amount of performance improvement of scenario 3 is fairly largerthan that of scenario 2. Therefore, choosing a suitable set ofabstracted parameters tuples is important in order to obtain largeperformance improvements while optimizing at low complexity. Also, theexperiments show that it is important to identify all degrees of freedomthat are available on the individual layers and to consider theimportant ones in the cross-layer design.

The present invention provides an architecture for the jointoptimization of application layer and radio link layer in a wirelesssystem with a video streaming service. This architecture is based onthree principle concepts, namely parameter abstraction, cross-layeroptimization, and decision distribution. Our preliminary study revealsthat the inventive architecture can provide a potential way to improvethe performance and therefore help dealing with the future challenge inwireless multimedia communication. Even when considering a small numberof degrees of freedom of the application layer and the radio link layer,we obtain significant improvements in user-perceived quality of ourstreaming video application by joint optimization.

Depending on certain implementation requirements of the inventivemethods, the inventive methods can be implemented in hardware or insoftware. The implementation can be performed using a digital storagemedium, in particular a disc or a CD having electronically readablecontrol signals stored thereon, which can cooperate with a programmablecomputer system such that the inventive methods are performed.Generally, the present invention is therefore a computer program productwith a program code stored on a machine-readable digital storage medium,the program code performing the inventive methods, when the computerprogram product runs on a computer. In other words, the inventivemethods are, therefore, a computer program having a program code for 5performing the inventive methods, when the computer program runs on acomputer.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents whichfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing the methods andcompositions of the present invention. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

1. An apparatus for controlling an operation of a plurality ofcommunication layers in a layered communication system, the layeredcommunication system transmitting information through a communicationchannel from a base station to a plurality of user devices, wherein theinformation comprises a first information associated with a first userdevice and a second information associated with a second user device ina multi-user scenario, wherein an operation of a first communicationlayer of the plurality of communication layers is determined by a firstset of parameters, and wherein an operation of a second communicationlayer, distinct from said first communication layer, of the plurality ofcommunication layers is determined by a second set of parameters,wherein the first communication layer is operative for encoding thefirst information to obtain a first information signal and for encodingthe second information to obtain a second information signal, andwherein the second communication layer is operative for encoding thefirst information signal and the second information signal to obtain acomposite signal to be transmitted through the communication channel,the apparatus comprising: a provider for providing a property of thecommunication channel; a storage element comprising a plurality ofjointly optimized sets of parameters, being optimized across the firstcommunication layer and the second communication layer, to be used indifferent scenarios, each scenario being defined by a predefinedtransmission quality for the first and second information and by apredefined communication channel property selected from the groupcomprising a bit error probability or/and a transmission delay or/and atransmission power associated with the bit error probability, or/and achannel coherence time or/and a channel coherence bandwidth, whereineach jointly optimized set of parameters comprises a pair of the firstand second set of pre-computed parameters defining the operation modefor the first and second communication layers for the associated one ofthe different scenarios; a selector for selecting from the storageelement directly one jointly optimized set of parameters dependent fromthe channel property the desired transmission quality for the firstinformation and for the second information; and a provider for providingthe first set of parameters and the second set of parameters from theselected jointly optimized set of parameters to the first communicationlayer and the second set of parameters to the second communicationlayer.
 2. The apparatus in accordance with claim 1, wherein the secondcommunication layer is operative for scheduling the first informationsignal and the second information signal, so that the first informationsignal is transmitted within a first time frame and the secondinformation signal is transmitted within a second time frame, whereinthe selector is operative for selecting the first set of parameters toobtain the first information signal having a first information rateassociated with a first distortion and to obtain the second informationsignal having a second information rate associated with the seconddistortion, and for selecting the second set of parameters for obtainingthe composite signal having a data rate supporting the first informationrate and the second information rate.
 3. The apparatus in accordancewith claim 1, wherein the first information associated with the firstuser comprises a first sub-information and a second sub-information,wherein the selector is further operative for selecting the first set ofparameters to be used by the first communication layer for selectivelyencoding the first sub-information and the second sub-information toobtain the first information signal comprising the encoded first andsecond sub-information.
 4. The apparatus in accordance with claim 2,wherein the selector is operative for selecting the first set ofparameters for scheduling the first sub-information and the secondsub-information within the first information signal, so that the firstsub-information and the second sub-information are placed at differentpositions of the first information signal.
 5. The apparatus inaccordance with claim 1, further comprising a determiner for determiningthe first communication layer of which the first set of parameters is tobe selected and the second communication layer of which the second setof parameters is to be selected from the plurality of communicationlayers to achieve the optimization goal.
 6. The apparatus in accordancewith claim 1, wherein the plurality of layers of the layeredcommunication system are protocol layers, wherein the secondcommunication layer is operative for managing a transmission of theinformation through the communication channel and for extracting theproperty of the communication channel, wherein the provider forproviding the property of the communication channel is coupled to thesecond communication layer for receiving the property of thecommunication channel.
 7. The apparatus in accordance with claim 6,wherein the second communication layer comprises a physical layer,wherein the provider for providing the property of the communicationchannel comprises a protocol interface for interfacing with the physicallayer.
 8. The apparatus in accordance with claim 1, wherein the selectorcomprises a decision element for monitoring a current status of thefirst communication layer determined by a coherent current first set ofparameters and a current status of the second communication layerdetermined by a current second set of parameters, wherein the decisionelement is further operative for generating a control information fromthe current statuses, from the optimization goal and from the channelproperty, wherein the control information indicates that the first setof parameters and/or the second set of parameters are to be selected toachieve the optimization goal, when the optimization goal cannot beachieved using the current first and second set of parameters.
 9. Theapparatus in accordance with claim 1, wherein the optimization goalcomprises the optimization of the transmission quality in a multi-userscenario, wherein the information comprises a first informationassociated with a first user and a second information associated withthe first user, a third information associated with a second user and afourth information associated with the second user, wherein the firstcommunication layer is operative for scheduling the first informationand the second information to obtain a first information signalassociated with the first user, and wherein the first communicationlayer is operative for scheduling the third information and the fourthinformation to obtain a second information signal associated with thesecond user, wherein the second communication layer is operative forscheduling the first information signal and the second informationsignal to obtain a scheduled multi-user stream, wherein the selector isoperative for jointly selecting the first set of parameters to be usedby the first communication layer to provide the first information signaland the second information signal, and the second set of parameters tobe used by the second communication layer to provide the scheduledmulti-user stream.
 10. The apparatus in accordance with claim 1, furthercomprising a provider for providing the optimization goal.
 11. Theapparatus in accordance with claim 1, wherein the second communicationlayer comprises a physical layer, wherein the first plurality of sets ofparameters stored in the storage element comprises a plurality ofmodulation schemes.
 12. The apparatus in accordance with claim 1,wherein the first or the second communication layer comprise a data linklayer, wherein the first plurality or the second plurality of parametersstored in the storage element comprise a plurality of forward errorcorrection encoding schemes.
 13. The apparatus in accordance with claim1, wherein the communication layer comprises an application layer,wherein the first plurality of sets of parameters stored in the storageelement comprises a plurality of encoding schemes for data compression.14. A communication apparatus for processing an information to betransmitted in accordance with a transmission protocol, the transmissionprotocol comprising a plurality of protocol layers, the communicationapparatus comprising: an information source for providing theinformation; an apparatus for controlling an operation of a plurality ofcommunication layers in a layered communication system, the layeredcommunication system transmitting information through a communicationchannel from a base station to a plurality of user devices, wherein theinformation comprises a first information associated with a first userdevice and a second information associated with a second user device ina multi- user scenario, wherein an operation of a first communicationlayer of the plurality of communication layers is determined by a firstset of parameters, and wherein an operation of a second communicationlayer, distinct from said first communication layer, of the plurality ofcommunication layers is determined by a second set of parameters,wherein the first communication layer is operative for encoding thefirst information to obtain a first information signal and for encodingthe second information to obtain a second information signal, andwherein the second communication layer is operative for encoding thefirst information signal and the second information signal to obtain acomposite signal to be transmitted through the communication channel,the apparatus comprising: a provider for providing a property of thecommunication channel; a storage element comprising a plurality ofjointly optimized sets of parameters, being optimized across the firstcommunication layer and the second communication layer, to be used indifferent scenarios, each scenario being defined by a predefinedtransmission quality for the first and second information and by apredefined communication channel property selected from the groupcomprising a bit error probability or/and a transmission delay or/and atransmission power associated with the bit error probability, or/and achannel coherence time or/and a channel coherence bandwidth, whereineach jointly optimized set of parameters comprises a pair of the firstand second set of pre-computed parameters defining the operation modefor the first and second communication layers for the associated one ofthe different scenarios a selector for selecting from the storageelement directly one jointly optimized set of parameters dependent froma first set of parameters from the first plurality of sets ofparameters, and for selecting the second set of parameters from thesecond plurality of sets of parameters, wherein the selector isoperative for selecting the first set of parameters and the second setof parameters in dependence of the channel property and the desiredtransmission quality for the first information and for the secondinformation, and wherein; and a provider for providing the first set ofparameters and the second set of parameters from the selected jointlyoptimized set of parameters to the first communication layer and to thesecond communication layer, for controlling the plurality of protocollayers; a processor for processing the information in accordance withthe protocol layers.
 15. A method for controlling an operation of aplurality of communication layers in a layered communication system, thelayered communication system transmitting information through acommunication channel from a base station to a plurality of userdevices, wherein the information comprises a first informationassociated with a first user device and a second information associatedwith a second user device in a multi-user scenario, wherein an operationof a first communication layer of the first plurality of communicationlayers is determined by a first set of parameters, and wherein aoperation of a second communication layer, distinct from said firstcommunication layer, of the plurality of communication layers isdetermined by a second set of parameters, wherein the firstcommunication layer is operative for encoding the first information toobtain a first information signal and for encoding the secondinformation to obtain a second information signal, and wherein thesecond communication layer is operative for encoding the firstinformation signal and the second information signal to obtain acomposite signal to be transmitted through the communication channel,the method comprising the following steps of: providing a property ofthe communication channel; storing in a storage element a plurality ofjointly optimized sets of parameters, being optimized across the firstcommunication layer and the second communication layer, to be used indifferent scenarios, each scenario being defined by a predefinedtransmission quality for the first and second information and by apredefined communication channel property selected from the groupcomprising a bit error probability or/and a transmission delay or/and atransmission power associated with the bit error probability, or/and achannel coherence time or/and a channel coherence bandwidth, whereineach jointly optimized set of parameters comprises a pair of the firstand second set of pre-computed parameters defining the operation modefor the first and second communication layers for the associated one ofthe different scenarios a first plurality of sets of parameters definingdifferent operation modes of the first communication layer; selectingfrom the storage element directly one jointly optimized set ofparameters dependent from the channel property and the desiredtransmission quality of the first information and of the secondinformation; and providing the first set of parameters and the secondset of parameters from the selected jointly optimized set of parametersto the first communication layer and to the second communication layer.16. A method for processing an information to be transmitted inaccordance with a transmission protocol, the transmission protocolcomprising a plurality of protocol layers, the method comprising thefollowing steps of: providing the information; controlling the pluralityof protocol layers in accordance with a method for controlling anoperation of a plurality of communication layers in a layeredcommunication system, the layered communication system transmittinginformation through a communication channel from a base station to aplurality of user devices, wherein the information comprises a firstinformation associated with a first user device and a second informationassociated with a second user device in a multi-user scenario, whereinan operation of a first communication layer of the first plurality ofcommunication layers is determined by a first set of parameters, andwherein a operation of a second communication layer, distinct from saidfirst communication layer, of the plurality of communication layers isdetermined by a second set of parameters, wherein the firstcommunication layer is operative for encoding the first information toobtain a first information signal and for encoding the secondinformation to obtain a second information signal, wherein the secondcommunication layer is operative for encoding the first informationsignal and the second information signal to obtain a composite signal tobe transmitted through the communication channel, the method comprisingthe following steps of: providing a property of the communicationchannel; storing in a storage element a plurality of jointly optimizedsets of parameters, being optimized across the first communication layerand the second communication layer, to be used in different scenarios,each scenario being defined by a predefined transmission quality for thefirst and second information and by a predefined communication channelproperty selected from the group comprising a bit error probabilityor/and a transmission delay or/and a transmission power associated withthe bit error probability, or/and a channel coherence time or/and achannel coherence bandwidth, wherein each jointly optimized set ofparameters comprises a pair of the first and second set of pre-computedparameters defining the operation mode for the first and secondcommunication layers for the associated one of the different scenarios;selecting from the storage element directly one jointly optimized set ofparameters dependent from the channel property and the desiredtransmission quality of the first information and of the secondinformation; and providing the first set of parameters and the secondset of parameters from the selected jointly optimized set of parametersto the first communication layer and to the second communication layer;processing the information in accordance with the protocol layer.
 17. Acomputer program stored on a computer-readable medium, said computerprogram having a program code for performing the method for controllingan operation of a plurality of communication layers in a layeredcommunication system, the layered communication system transmittinginformation through a communication channel from a base station to aplurality of user devices, wherein the information comprises a firstinformation associated with a first user device and a second informationassociated with a second user device in a multi-user scenario, whereinan operation of a first communication layer of the first plurality ofcommunication layers is determined by a first set of parameters, andwherein a operation of a second communication layer, distinct from saidfirst communication layer, of the plurality of communication layers isdetermined by a second set of parameters, wherein the firstcommunication layer is operative for encoding the first information toobtain a first information signal and for encoding the secondinformation to obtain a second information signal, and wherein thesecond communication layer is operative for encoding the firstinformation signal and the second information signal to obtain acomposite signal to be transmitted through the communication channel,the method comprising the following steps of: providing a property ofthe communication channel; storing in a storage element a plurality ofjointly optimized sets of parameters, being optimized across the firstcommunication layer and the second communication layer, to be used indifferent scenarios, each scenario being defined by a predefinedtransmission quality for the first and second information and by apredefined communication channel property selected from the groupcomprising a bit error probability or/and a transmission delay or/and atransmission power associated with the bit error probability, or/and achannel coherence time or/and a channel coherence bandwidth, whereineach jointly optimized set of parameters comprises a pair of the firstand second set of pre-computed parameters defining the operation modefor the first and second communication layers for the associated one ofthe different scenarios; selecting from the storage element directly onejointly optimized set of parameters dependent from the channel propertyand the desired transmission quality of the first information and of thesecond information; and providing the first set of parameters and thesecond set of parameters from the selected jointly optimized set ofparameters to the first communication layer and to the secondcommunication layer, when the program runs on a computer.
 18. A computerprogram stored on a computer-readable medium, said computer programhaving a program code for performing the method for processing aninformation to be transmitted in accordance with a transmissionprotocol, the transmission protocol comprising a plurality of protocollayers, the method comprising the following steps of: providing theinformation; controlling the plurality of protocol layers in accordancewith t4˜-amethod for controlling an operation of a plurality ofcommunication layers in a layered communication system, the layeredcommunication system transmitting information through a communicationchannel from a base station to a plurality of user devices, wherein theinformation comprises a first information associated with a first userdevice and a second information associated with a second user device ina multi-user scenario, wherein an operation of a first communicationlayer of the first plurality of communication layers is determined by afirst set of parameters, and wherein a operation of a secondcommunication layer, distinct from said first communication layer, ofthe plurality of communication layers is determined by a second set ofparameters, wherein the first communication layer is operative forencoding the first information to obtain a first information signal andfor encoding the second information to obtain a second informationsignal, wherein the second communication layer is operative for encodingthe first information signal and the second information signal to obtaina composite signal to be transmitted through the communication channel,the method comprising the following steps of: providing a property ofthe communication channel; storing in a storage element a plurality ofjointly optimized sets of parameters, being optimized across the firstcommunication layer and the second communication layer, to be used indifferent scenarios, each scenario being defined by a predefinedtransmission quality for the first and second information and by apredefined communication channel property selected from the groupcomprising a bit error probability or/and a transmission delay or/and atransmission power associated with the bit error probability, or/and achannel coherence time or/and a channel coherence bandwidth, whereineach jointly optimized set of parameters comprises a pair of the firstand second set of pre-computed parameters defining the operation modefor the first and second communication layers for the associated one ofthe different scenarios; selecting from the storage element directly onejointly optimized set of parameters dependent from the channel propertyand the desired transmission quality of the first information and of thesecond information; and providing the first set of parameters to thefirst communication layer and the second set of parameters from theselected jointly optimized set of parameters and to the secondcommunication layer; processing the information in accordance with theprotocol layer, when the program runs on a computer.
 19. The apparatusin accordance with claim 1, wherein the first and second set ofpre-computed parameters defining the operation mode for the first andsecond communication layers for the associated one of the differentscenarios are computed by a first abstraction model and a secondabstraction model and a cross-layer optimizer, each abstraction modelcausing a parameter abstraction to transform the communication layerspecific first and second parameters into first and second keyparameters comprehensible for the cross-layer optimizer; wherein thefirst abstraction model causes a first communication layer parameterabstraction to define a plurality of first key parameters beingdescribed by one or more parameters of said first parameters, and thesecond abstraction model causes a second communication layer parameterabstraction to define a plurality of second key parameters beingdescribed by one or more parameters of said second parameters, andwherein the cross-layer optimizer jointly determines the optimized setof parameters to be used by the first communication layer and the secondcommunication layer based on the first and second key parameters, thechannel property and the desired transmission quality.
 20. Thecommunication apparatus in accordance with claim 14, wherein the firstand second set of pre-computed parameters defining the operation modefor the first and second communication layers for the associated one ofthe different scenarios are computed by a first abstraction model and asecond abstraction model and a cross-layer optimizer, each abstractionmodel causing a parameter abstraction to transform the communicationlayer specific first and second parameters into first and second keyparameters comprehensible for the cross-layer optimizer; wherein thefirst abstraction model causes a first communication layer parameterabstraction to define a plurality of first key parameters beingdescribed by one or more parameters of said first parameters, and thesecond abstraction model causes a second communication layer parameterabstraction to define a plurality of second key parameters beingdescribed by one or more parameters of said second parameters, andwherein the cross-layer optimizer jointly determines the optimized setof parameters to be used by the first communication layer and the secondcommunication layer based on the first and second key parameters, thechannel property and the desired transmission quality.
 21. The method inaccordance with claim 15, wherein the first and second set ofpre-computed parameters defining the operation mode for the first andsecond communication layers for the associated one of the differentscenarios are computed by a first abstraction model and a secondabstraction model and a cross-layer optimizer, each abstraction modelcausing a parameter abstraction to transform the communication layerspecific first and second parameters into first and second keyparameters comprehensible for the cross-layer optimizer; wherein thefirst abstraction model causes a first communication layer parameterabstraction to define a plurality of first key parameters beingdescribed by one or more parameters of said first parameters, and thesecond abstraction model causes a second communication layer parameterabstraction to define a plurality of second key parameters beingdescribed by one or more parameters of said second parameters, andwherein the cross-layer optimizer jointly determines the optimized setof parameters to be used by the first communication layer and the secondcommunication layer based on the first and second key parameters, thechannel property and the desired transmission quality.
 22. The method inaccordance with claim 16, wherein the first and second set ofpre-computed parameters defining the operation mode for the first andsecond communication layers for the associated one of the differentscenarios are computed by a first abstraction model and a secondabstraction model and cross-layer optimizer, each abstraction modelcausing a parameter abstraction to transform the communication layerspecific first and second parameters into first and second keyparameters comprehensible for the cross-layer optimizer; wherein thefirst abstraction model causes a first communication layer parameterabstraction to define a plurality of first key parameters beingdescribed by one or more parameters of said first parameters, and thesecond abstraction model causes a second communication layer parameterabstraction to define a plurality of second key parameters beingdescribed by one or more parameters of said second parameters, andwherein the cross-layer optimizer jointly determines the optimized setof parameters to be used by the first communication layer and the secondcommunication layer based on the first and second key parameters, thechannel property and the desired transmission quality.
 23. The computerprogram in accordance with claim 17, wherein the first and second set ofpre-computed parameters defining the operation mode for the first andsecond communication layers for the associated one of the differentscenarios are computed by a first abstraction model and a secondabstraction model and a cross-layer optimizer, each abstraction modelcausing a parameter abstraction to transform the communication layerspecific first and second parameters into first and second keyparameters comprehensible for the cross-layer optimizer; wherein thefirst abstraction model causes a first communication layer parameterabstraction to define a plurality of first key parameters beingdescribed by one or more parameters of said first parameters, and thesecond abstraction model causes a second communication layer parameterabstraction to define a plurality of second key parameters beingdescribed by one or more parameters of said second parameters, andwherein the cross-layer optimizer jointly determines the optimized setof parameters to be used by the first communication layer and the secondcommunication layer based on the first and second key parameters, thechannel property and the desired transmission quality.
 24. The computerprogram in accordance with claim 18, wherein the first and second set ofpre-computed parameters defining the operation mode for the first andsecond communication layers for the associated one of the differentscenarios are computed by a first abstraction model and a secondabstraction model and a cross-layer optimizer, each abstraction modelcausing a parameter abstraction to transform the communication layerspecific first and second parameters into first and second keyparameters comprehensible for the cross-layer optimizer; wherein thefirst abstraction model causes a first communication layer parameterabstraction to define a plurality of first key parameters beingdescribed by one or more parameters of said first parameters, and thesecond abstraction model causes a second communication layer parameterabstraction to define a plurality of second key parameters beingdescribed by one or more parameters of said second parameters, andwherein the cross-layer optimizer jointly determines the optimized setof parameters to be used by the first communication layer and the secondcommunication layer based on the first and second key parameters, thechannel property and the desired transmission quality.